In the real subs, the dive time was from giving the order to periscope depth. And for them, there was no such thing as a crash dive. Every dive was a crash dive, which was a normal dive.
In the game, periscope depth is a bad thing because the boat actually starts to level out before it is fully submerged, making dives using the P key really slow. I've noticed that although the diving officer reliably calls out the 40' mark, he doesn't always do it at the same time, as his call can be interrupted by other events going on at the same time. I suppose in controlled test conditions that might not be a problem.
But I'd be inclined to use the depth gauge and use 60' as my timing, to correspond with the real submariner's use of periscope depth. They would yo-yo through the depth on their timing runs, overrunning and coming back up to actually use the periscope. We can do the same thing by using C and hitting P as we break 40'. For timing purposes, though, I wouldn't hit P at all, just stop the clock when the sub passes 60'.
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