That method is an old one, from back when the computers weren't quite so "efficient" with their then-meager resources. Older computers would "hiccup" with certain aspects of the game, but the newer computers don't so much.
Depending upon the mods you're using, if any, planes can see you down to 120-160 foot roughly. In stock, anything below PD will usually work. Dying while in TC can be any one of a number of things. There are a lot of ways to die in SH4. CO2 asphyxiation is one, smacking the ocean floor, hitting a mine (not so much in stock trim), planes or DD that detect you, etc, but especially so in enemy waters. TC in SH4 does not work as we'd like. You'd think it'd have a "look-ahead", but apparently doesn't. I did the math a few months ago over in the
Fall of the Rising Sun Ultimate thread, and it's really kind of scary how much time can pass and how far your boat will travel at even lower compression settings. As an example, at 512x TC, your boat traveling at 2 knots, will travel 3.37555 feet per second of actual time, or 1728.28444 in that 512x TC. Say you're using that 1556x TC figure, three times that of 512x, and you've traveled 5184.85+ feet - one hundred feet short of a land mile. An hour's time passes in 2.31 seconds at that rate, about 26 minutes per second, correct? (I am not good at math this early - or ever, for that matter.) The game does not "detect" airplanes overhead when you're submerged until the first bomb drops, and the crew goes "We're under attack, sir!" You come out of time compression, and you're sunk already. 2048x TC is where you get the stopwatch to open, and you can lower from there and it'll stay open, but TC hiccups are not the way to find the enemy anymore.
If you have a sub with radar, it's better to do this:
Again, depending upon the mods used, you may have to make the "visual" circle a little bigger. Also, be sure your deck watch are the best "eyes" in the crew. Look at the crewmembers' ratings on the crew page.
If you "shell out" from the game in Windows, using the <Alt><Tab>, or the Windows key, or whatever, that will cause the game to "stick" on certain aspects, such as the CO2 levels will not decrease when you surface the boat, and will continue to rise, and when you submerge for your 2nd day's journey... the next thing you know, you're crew is dead, with no "warning" - other than that little flashing thingie in the upper right of the screen, which can be difficult to see in a submerged boat's interior... When things get stuck like that, you have to Save the game and exit out. Re-start the game and load your Save to continue.