Instead of a 32 bit int describing the combined year and time, you could make two ints: $year and $time. Or perhaps better: look in CPAN for time/date modules that can describe this concept with a more complex data structures.

Doing "date/time" math can be more complex than you might think. For a small example, this year (2012) - we had a "leap second" - WOW - what the heck does that mean?.

I didn't mean to make a pun. But think about this and what might happen in 2106?