Perusall sends email reminders to students 3 days, 2 days, and 1 day before the deadline of an assignment. Only students that have not started an assignment (or still have a grade of 0) will be sent a reminder.

Reminders are enabled by default, but you can disable reminders for your course by unchecking Enable assignment reminders under Settings > Advanced.

Students can also individually opt out of receiving such reminders by clicking Notifications > Manage notifications, and then unchecking Notify me when an assignment that I haven't yet completed is about to be due.