My tip:
Dang if they are gonna leave me behind in port when the fun begins...
I adjust time in port with SHCommander so I am back and well out to sea in the on the 1st of September, scouting the Kagerrak before heading for my assigned area.
..and readjust when I get back so I am back on the normal 28 day schedule.
Also works when Weserübung is afoot. For some reason the Sim seems to conspire to keep you out of that action by having you arrive too late if you stay with the normal 28 day schedule.