When you enable backups for a Droplet, you can choose between daily and weekly backups, but you cannot change the backup window.
You can back up your Droplet at any time using snapshots. Snapshots create an image of the Droplet the same way a backup does, but snapshots persist on your account even if the Droplet is destroyed. You can also automate taking snapshots using the DigitalOcean API, or use SnapShooter.