Not at the moment. Messages can't be scheduled to send at a specific time.
When you send a message, the participant receives it immediately, including an SMS notification. So it's worth being mindful of participants' local time before hitting send, especially on international studies. See How do timezones work on Askable?
If you need a message to go out at a set time, the current workaround is a calendar reminder for yourself to send it then.
We're always improving messaging, so this may change. For anything urgent that needs precise timing, message us on live chat and we can help coordinate.