Ah, TC = Time Compression

I think x16 is ok, x32 will 'magically' make the escorts return directly over my position.
As I played again a career with 95% realism I discovered some oddities in game play (In Realism, I leave the depth under keel gauge active to compensate for the patrol map that lacks precise depth data, contrary to real skippers which probably had much better data. This will only cost me 5%).
Here some additional notes:
Straights:
You cannot navigate through some narrow straights (e.g. Sea of Japan) because the depth under keel is not enough even when surfaced. The only way to find out about those straights is to do some recon after setting up a hand-made mission (with the editor).
Bug: Escorts are not aggressive when you do surface escapes:
If you are further away than 2000 yards, escorts that have spotted you and are heading towards you will not fire, but you can fire at them with your deck gun... about 8 hits will reduce their speed enough so you can escape. At some point make a 60° turn to see if they will follow you, if not they have lost contact and go on straight for quite a while.
So, for realism, just DON'T DO all this and dive if they spot you.
Visibility:
Your sub's visibility is not just a factor of your speed, aspect angle and weather/sea conditions. Good trained escorts may spot you at much further distances even at night. As said above be careful with moon light.
Bug: Magic periscope:
You can raise your periscope after dawn / sunrise and still see something (the map will also show precise ship positions).
Bud Gruner clearly stated that scopes were useless at night. Again, for realism, DON'T USE YOUR SCOPE at night.
Bug: Ship ID book
This is well-known: don't leave your ship ID book open or the game will crash (Commander 1.3 edition).
XS