[Spraug]

To achieve the objectives, you have to stay close to the indicated points for a period of time. From your description I guess you are using plain vanilla version (no mods) so the range should be 50nm around the point and I guess you have to stay 24hours in this radius. While I'm not sure about the two figures, the critical point is that the time returns to zero if you leave the area in between, so just stay close to the binoculars sign until you get the message that the objective was fulfilled.

The really interesting part, however, is what depthtok said (typed): You are given objective, but they don't play a role for patrol evaluation. You can be assigned an area around Singapore and still get a Navy Cross/MoH without ever going South of Honshu if you sink a bucket full of ships.

Your 100kt will insure that the brass back home will love you, no matter how many objectives are still open.