Can we select departure date with 3 nights default?

Yes, we can set the default departure date with 3-nights one you select an arrival date.

That can be done from old extranet >> Settings >> Booking page >> Booking engine settings.

If you have a booking box-like (below screenshot) on your web booking page and you set 3 Number in cut off Days, which means 3 day’s stay will be by default on all stay.