[Dogfish40]

I think I touched this subject in another post, but not as a direct question.
Knowing I am playing a game, at the same time I'm a bit of a History student, I keep restarting my career for various reasons, (mostly getting the mods tweaked in just right). The question is, in Aug 8, 1939 I'm sent out on patrol. The mission orders state "1st and 2nd Flotillas should go out on a 5 day Shakedown then come back in." 3rd Flotilla whatever, I need only know the 2nd which is mine.
Since the U-Boats (Historically) did not put out to sink British merchant shipping until Sep 3, 39, should I be sinking anything??
The notes refer to enemy shipping and give me a patrol sector of BF16 or something, a five day shakedown doesn't specify to sink enemy shipping.
The reason of my concern is, I don't want to lose renown for sinking ships before hostilities start.
What do you think? Am I too serious about the dates or should I hold fire until September?
Thanks
D40