Send time accounts for ~15% of the variance in reminder open rates. Worth getting right.
The optimal windows
| Reminder type | Best window | Avoid |
|---|---|---|
| 24h before appointment | 6-8pm | Office hours, late night |
| Day-of (morning slot) | 8-9am | Before 7:30am |
| Day-of (afternoon slot) | 2 hours before | During lunch (1-2pm) |
| Follow-up reminder | 10-11am on a Tuesday or Thursday | Monday morning, weekends |
| Recall to lapsed patient | Saturday morning | Sunday evening |
Why these windows
- 6-8pm: workday is over, household is settled, phone use peaks.
- 8-9am: morning routine, alarm just went off, planning the day.
- Tuesday/Thursday 10-11am for follow-ups: weekday work-from-office checked-in but still alert.
- Saturday morning for recall: weekend energy, time to make decisions about health.
What kills response rates
- Sending before 7:30am: feels intrusive.
- Sending after 9pm: lower visibility AND complaint risk.
- Sending during lunch (1-2pm): low open rate.
- Sending Monday morning for non-urgent reminders: blends into work-week noise.
Vaidya OS auto-schedules reminders to optimal windows by reminder type.