How Klaviyo Smart Send Time Works and What to Use in Flows

Klaviyo's send time optimization feature, Smart Send Time, works in campaigns, where it runs a timed experiment across your list and reports one best hour, and we found no version of it for flows in the help center pages we read. Teams lose hours on this because four features carry near-identical names. Smart Send Time is the campaign experiment. Personalized Send Time is a per-profile scheduler, also limited to campaigns. Smart Sending is a frequency cap. Time delays are the only one of the four that decides when a flow message leaves, so the working pattern is to find your hour in campaigns and set it by hand on the delay.

How does Klaviyo send time optimization work in campaigns?

Klaviyo send time optimization works as a test on your own sends, run in three phases that the Klaviyo Help Center overview (updated Mar 26, 2026) names exploratory, focused and optimal.

In the exploratory phase a campaign goes out over a 24-hour period, each recipient is randomly assigned a time within it, and every email is sent in the recipient's local time. The number of exploratory campaigns required depends on audience size:

The overview's FAQ sets the floor: "Smart Send Time exploratory and focused sends are only available for campaigns with 12,000+ recipients."

The focused phase validates the winner. Per the Klaviyo testing guide, emails go out at the best time from the exploratory data, plus two hours before and two hours after. Once found, the hour is no longer tied to big sends, since the overview states that "Optimal send time can be used for audiences of any size." A campaign scheduled this way sends at that hour in each recipient's local time zone, so it can take up to 24 hours to finish.

Three details from the same overview are easy to miss. The model waits out your conversion period (five days by default) before it records a campaign, so results arrive slowly. A Smart Send Time email cannot be A/B tested. Klaviyo advises against time-sensitive content such as a flash sale, since delivery follows local time. A caution of our own: the report graphs open rate per hour, so confirm the winning hour against clicks and orders in your own campaign data.

Can you use Klaviyo Smart Send Time in flows?

Klaviyo Smart Send Time in flows is something we found no support for in the help center. The overview describes the feature in terms of campaigns and says it is only available for email, and the testing guide adds that it cannot be used for SMS or push campaigns. We also read the Klaviyo page on flow email settings, which lists three: a "Skip recently emailed profiles" checkbox, UTM tracking and additional filters. We found no send-time option among them, so plan as if the experiment stops at the campaign scheduler.

Is there AI send time optimization for flows in Klaviyo?

Klaviyo's AI send time optimization for flows is not available yet, going by the vendor's own page. The closest product is Personalized Send Time. The Klaviyo article on it (updated Aug 26, 2026) describes a feature that schedules each campaign message at every recipient's predicted best time inside a delivery window you choose, using reinforcement learning on past engagement behavior and similar profiles. That same page states: "Personalized Send Time is not available yet in flows."

For campaigns, four conditions matter before you plan around it:

• Klaviyo offers it on the Marketing Analytics or Advanced Klaviyo Data Platform packages, which it says are not included in its standard marketing application and need a subscription.
• It covers email, SMS, push and WhatsApp campaigns.
• Same-day sends are out: "You must schedule campaigns at least one day in advance."
• Smart Sending is evaluated at each message's real send time, so a recipient who already got another message inside your window may be skipped.

Which settings control when a flow message sends?

The official documentation for a scheduled send time in a Klaviyo flow is the flow delay article, since the time delay is where the clock gets set. The Klaviyo Help Center guide to time delays lists waits in minutes, hours or days, plus a wait in days that holds until a specific time of day. The same component carries a time zone selector (the guide points to "Recipient's Local Timezone") and a day-of-week option that starts with all days selected. We found no statement there on whether a set time and specific days combine on one delay, so check the builder first.

Three behaviors decide whether the hour you typed is the hour people get:

1. Day counting changes when you add a time. A plain day is a 24-hour period, and a day with a set time is a calendar day. In Klaviyo's example of a one-day wait until 3 PM, someone who enters at 2 PM and someone who enters at 4 PM both get the email at 3 PM the next day, the second person 23 hours after triggering the flow.
2. Local time has a fallback. The guide says: "If the profile's timezone cannot be accurately determined, your account's timezone will be used."
3. Nothing waits without a delay. Components placed back to back with no time delay all occur simultaneously, and a delay must be followed by a flow action in live or manual status.

Klaviyo also notes that a plain wait in days, with no set time, delivers the message at the same time of day the recipient took the trigger action. We treat that as a per-person send hour you get for free, which is why early steps in the setup below stay on relative timing.

A flow timing setup you can copy

An implementation of AI send-time optimization in Klaviyo flows is manual today, going by the help center pages we read: you borrow the hour from your campaign test and type it into the delay. The setup below is a hypothetical example for an ecommerce account. The delay lengths and the 10 AM hour are our illustrative assumptions, so substitute the hour from your own Smart Send Time report.

Messages tied to a fresh action keep relative timing, because the trigger tells you more about that person's day than a list-wide average does. Messages with no urgency get pinned to the tested hour in local time. To challenge the assumed delays, the Klaviyo flow frequency guide publishes a chart of recommended frequencies and suggests A/B testing flow branches with different time delays. Our lifecycle email playbook is a further resource for the wider program, and the lifecycle and demand generation team builds this kind of setup.

What does Smart Sending do to flow email timing?

Smart Sending is the official Klaviyo setting that gets mistaken for send time optimization on a flow email, and it does a different job: it limits how many messages a person can receive within a set period. The Klaviyo Help Center article on Smart Sending gives default windows of 16 hours for email, 24 hours for SMS and 24 hours for push notifications.

Campaigns have it enabled by default. For flows, the two pages we read come at it from different sides. The Smart Sending article says "Smart Sending is enabled for flow messages in many pre-built flows." The flow frequency guide says "Flow messages will not enable Smart Sending by default." The safe move is to open every flow message and look at the "Skip recently emailed profiles" checkbox yourself.

What matters for timing is one line of the Smart Sending article: "Messages skipped due to Smart Sending are not rescheduled automatically." For that reason the table turns it off on the first welcome and first cart emails, where a lost message costs more than two emails in one day. That is our judgment for those two messages; Klaviyo's general recommendation is to keep Smart Sending on for most, if not all, marketing emails.

Plan for one collision. If campaigns and pinned flow emails share the tested hour, whichever message reaches a profile second falls inside the 16-hour default window and, by our reading of the documented behavior, is skipped when Smart Sending is on for it. Offsetting the flow hour from the campaign hour avoids that, and on low-priority messages you may decide the skip is acceptable.

Text messages pass one more gate. The Klaviyo article on text message quiet hours in flows says a recipient whose text comes due during quiet hours goes into a Waiting queue until the next available sending time, and it lists before 8 a.m. and after 9 p.m. as quiet hours for countries including the US and Canada, with a note that several US states such as Florida limit sending to between 8 a.m. and 8 p.m. We found no equivalent quiet-hours or send-window setting for flow emails in the pages we read.

Where send time sits next to deliverability

Send time is a second-order lever. An email filtered to spam at the perfect hour is unlikely to be read, so settle inbox placement first: start with what email deliverability is, and treat the email deliverability checker as a further resource. Our email marketing statistics roundup gives context for open and click rates, and if Personalized Send Time has you pricing add-on packages, what email marketing costs covers the platform and labor lines.

Run the campaign test once a send clears 12,000 recipients, write the hour down, and revisit every pinned flow delay whenever that report changes. Until Klaviyo brings either feature to flows, the delay is where the optimization lives.

Sources

• Klaviyo Help Center: Understanding Smart Send Time in Klaviyo (updated Mar 26, 2026)
• Klaviyo Help Center: How to perform and analyze Smart Send Time tests (updated Jul 7, 2025)
• Klaviyo Help Center: Drive performance with right time delivery using Personalized Send Time (updated Aug 26, 2026)
• Klaviyo Help Center: How to add a time delay to a flow (updated Jul 7, 2025)
• Klaviyo Help Center: Understanding Smart Sending in Klaviyo (updated Aug 6, 2025)
• Klaviyo Help Center: How to optimize your flow sending frequency (updated Jul 24, 2025)
• Klaviyo Help Center: How to review a flow email's settings (updated Jul 7, 2025)
• Klaviyo Help Center: Understanding text message quiet hours in flows (updated Sep 10, 2026)