Backup Configuration Files > scheduled backups > Edit Scheduled Backup.backup now
if the jscript = Backup schedule is not in the open mode (not collapsed) then the error =Failed to save backup : You did not choose any Minutes to execute= is generated.
this is probably normal and expected, even correct. but the less informed may not know that the settings are not being submitted in the collapsed mode.
Do you see this when editing an existing backup, or creating a new one?