When you schedule backups in Modular DS, the time zone used to define the backup schedule matches the time zone of your web browser at the time of access. 

This means that the system automatically adjusts the backup schedule according to your device's time zone, without the need for you to make any manual selections, so that backups are performed at times that best suit your location.

You will be able to see which time zone is being used in the recurrence section of the backup settings:

Backup time zone