We've re-written the system that sends reminders for bookings. The system has sent these since the beginning, but early in 2019 a powerful general purpose system under Admin > Reminders & follow-ups was developed. This is where all your follow-up emails to students etc and reminders are managed. And it's a better system for handling booking reminders.
You could use the system to send more than one reminder, perhaps one a week before and another 24 hours before. Each message can be customised independently.
Plus it gives you visibility into these messages. You can view reminders that have been sent and those still in the queue from the configuration page.
Note: You can click the totals at the bottom (41, 25) to view all messages sent or queued.