Actually, this is a damn bug in SOF.
To complete this mission in less time, go to patrol area 2 FIRST. You have the chance to sink a "Lion"-class battlecruiser there.
THEN go to patrol area 1 and wait in the UPPER LEFT QUARTER until patrol time is over.
If the "Gneisenau"-cruiser appears then, it will take "only" circa 45-60 minutes on 16x to reach Wilhelmshaven.
It's stupid, but the only way.
Greets