Scheduling a live lets followers find it in advance and get notified when it starts.
Schedule it
Open Live and choose Scheduled live.
Upload a thumbnail image (1080 x 1920).
Add a short preview video announcing your live. It shows in the feed until the live starts.
Choose the date and time, then finish the remaining steps.

Before it starts
ReUp emails you a confirmation and a reminder 30 minutes before you start. Followers see Starting Soon and can choose Notify me when it's live.