Hi YoYo
Yes, that is correct.
The missions are date controlled.
Eastern British Coastal (EBC) starts on 04/09/39 but does not finish until 01/12/39.
You will then see Breaking The Fortress (BTF) appear on 10/09/39 possibly while you are at sea heading towards EBC.
This has a limited time to complete until 15/10/39
Personally BTF is disappointing and I no longer do it as the escorts do not respond in Scapa as they should to sinking a capital ship.
Missions appear as in the picture (start date) and disappear (end date) with new ones also appearing as well.
The picture shows 3 missions all active within their dates
Each time you end the patrol and start the same one you will get a new patrol area.
Each completed patrol area is worth 1 bonus point that can be used on Crew abilities.
In the picture there are 2 mission choices to consider EBC 04/09/39 to 01/12/39 and NWA 21/09/39 to 01/04/40.
If you are short of tonnage in EBC then that is the one to choose.
Do a manual save in the bunker each time before starting the mission again.
The important thing to remember is to end the patrol after a new mission appears or you will not be able to select it.
Each time you end a patrol the time advances by 28 days.
Peter