- Android: Your photos are backed up as you take them (can be limited to Wi-Fi)
- Mac/PC: Your photos are being backed up continuously. If you add new photos to one of the backup folders they will automatically start syncing. To track progress, open Shoebox and check the "Settings" page.
- iPhone/iPad: Your photos are backed up when you launch the app (can be limited to Wi-Fi). They are also occassionaly backed up in the background, but the exact schedule is controlled by Apple.
For details on background upload on iOS, see the question: 'How do I ensure my iPhone/iPad continues to backup new photos in the background?'