We have made several changes to our Droplet Scheduling to provide better scale and service and spread our peak loads.
Droplets will be scheduled in advance of their slot and shown in the UI. This can happen up to 40 minutes before the backup window. The scheduler has built redundancy to attempt to schedule the backup multiple times before the backup slot.
During the backup window, your backup will start; for free customers within an hour slot and paid users within 15 minutes.