Definition
Send time testing determines the optimal delivery time for each subscriber or segment by analysing historical engagement patterns. Unlike send-time optimisation (STO), which uses algorithms to predict optimal times, send time testing uses controlled experiments — sending the same email at different times to different groups — to identify timing preferences.
Optimal send time varies by audience, industry, and individual subscriber behaviour. B2B audiences typically engage during business hours (Tuesday–Thursday, 8am–12pm). B2C audiences engage more during evenings and weekends. Individual subscribers may have unique patterns based on their schedule, timezone, and habits. Testing reveals what works for your specific audience.
Send Time Testing Approaches
| Approach | Method | Best For |
|---|---|---|
| A/B time test | Split list, send at 2 different times | Identifying best general send time |
| Multi-wave test | Send in waves at different times | Testing 3–5 time options |
| STO (algorithmic) | ML predicts per-subscriber optimal time | Personalised send times at scale |
| Timezone sending | Adjust send time per recipient timezone | Geographic audience distribution |
Best Practices
- Test send time against your specific audience — general industry benchmarks may not apply to you
- Run send time tests for at least 2 weeks to account for day-of-week variations
- Measure performance by click rate and conversion rate, not just open rate (MPP inflation)
- Consider timezone differences — a subscriber in New York and London have a 5-hour gap
- Segment send time testing by audience type (B2B vs B2C, engaged vs casual)
- Re-test send time quarterly — subscriber behaviour changes over time
- Combine send time testing with frequency testing for comprehensive timing optimisation
Related Glossary Terms
Delay Send
Delay send is an email feature that holds a message for a specified period before delivery, allowing send-time optimisation, scheduled campaigns, or last-minute edits before an email goes out.
Email Scheduling
Email scheduling is the practice of setting a specific future date and time for an email campaign to be sent, ensuring optimal delivery timing without manual intervention.
Timezone-Based Email Sending
Local time delivery for email campaigns using subscriber timezone detection via IP geolocation, browser timezone, and profile data. Send window optimisation and typical engagement lift of 5-15%.
Recency Bias in Email Marketing
Recency bias is the tendency to overweight recent information over historical data, used in email marketing to time campaigns for maximum impact on subscriber decision-making.
Frequently Asked Questions
There is no universal best day — it depends on your audience and industry. General benchmarks (Tuesday–Thursday) are starting points, not rules. The best approach is to test different days with your specific list and identify what drives the highest engagement for your audience.
Run send time tests for at least 2–4 weeks to capture day-of-week patterns and account for weekly variations. Shorter tests may be skewed by day-specific factors. For statistically significant results, ensure each test group has at least 1,000 subscribers per variation.