You absolutely can customize 2 different email reminders on different times. You start by going to “Settings” tab and click on “Customize Emails/Text”:
Choose “Booking Reminder”:
Since you already have an existing Booking Reminder set up on your account, you can then click on the option “Add Another Reminder”:
You will then be lead to another page where you can set the time of when you want this booking reminder to be sent and the content of the booking reminder email:
Hit “Save Reminder” to save the changes you made.