Just open it as a binary file in python (or your language of choice).
There are a few parts with the name of your submarine-type (e.g. SSTypeVIIB) - you'll see it with a hex editor. Offset from the first one, at 330 bytes after the end of the submarine-type, is a pair of words with the year (e.g. \x07\x94 which is 1940: see
http://coolconversion.com/math/binar...n_hexadecimal_)
After that comes the month, day, hour and minute (although the latter can be off by one if the minute has just changed).