In addition to the foregoing, consider packages such as Date::Calc and Date::Manip.   Packages like these can be useful in situations such as, for example, reliably processing a Unix timestamp-value on a Win32 system, or writing platform-independent code that doesn’t have to care.

There are also logfile-format specific routines that are intended to simplify processing of these files in a more general sense.   You might discover that even more of your problem has already been solved by others than you might initially have assumed ... which is always a very nice discovery to make.