Please read the manual :
How to define a backup window?
In the settings you can set a backup window. The server will only start backing up clients within this window. The clients can always start backups on their own, even outside the backup windows. If a backup is started it runs till it is finished and does not stop if the backup process does not complete within the backup window. A few examples for the backup window:
1-7/0-24: Allow backups on every day of the week on every hour.
Mon-Sun/0-24: An equivalent notation of the above
Mon-Fri/8:00-9:00, 19:30-20:30;Sat,Sun/0-24: On weekdays backup between 8 and 9 and between 19:30 and 20:30. On Saturday and Sunday the whole time.
As one can see a number can denote a day of the week (1-Monday, 2-Thuesday, 3-Wednesday, 4-Thursday, 5-Friday, 6-Saturday, 7-Sunday). You can also use the abbreviations of the days (Mon, Thues, Wed, Thurs, Fri, Sat, Sun). The times can either consist of only full hours or of hours with minutes. The hours are on the 24 hour clock. **
u can set multiple days and times per window definition, separated per “,”. You can also set multiple window definitions. Separate them with “;”.