Whether or not you have an RSVP deadline set on your event, auto-reminders are sent 1 week before the event to "Invited" and "Maybe" guests, and 2 hours before the event to "Going" guests. You can view this schedule in your event settings.
If your RSVP deadline is more than 1 week before your event, guests won't receive any reminders to RSVP. Instead, you can send a reminder yourself using a Text Blast!