Yes, absolutely. You can set the exact number of minutes prior to each appointment that reminder text messages and/or emails should go to your clients.
Go to Settings -> Customize Emails/Texts:
Then from the list of the different message types, click on the customize button next to "Booking Reminder".
You will see the page where you can edit the content of the reminder email and text messages. You will also see a field that you can enter how many minutes before each appointment the reminders should go out. Click on the "Edit" button to proceed: