Not sure about configuring it via files, but you can overlay the default Granite config to change the daily window.
To change the start and end times, create a new sling:OrderedFolder with the name 'granite:daily' under /apps/granite/operations/config/maintenance, then add 'windowStartTime' with a String value of the time to start and 'windowEndTime' with a String value of the time to end.
See the default config here as a reference: /libs/granite/operations/config/maintenance/granite:daily