• Quick, not very tidy and probably quite slow for many calls for different dates:


• Figure out the time for Jan 1 2002, 0000hrs 0 sec and Jan 2 2002 0000hrs 0 sec and then check to see if the database time is between that.


• Properly:


• Hit CPAN, grab Date::Calc and knock together a script using that module
• If it's a proper database (i.e. an RDBMS, not some CSV files), use the power of the database to do all this for you.

Update: And if possible, it's probably a good idea to insert dates into the database using the database's native representation of date/time - then all this stuff can be done in the database.
If it's something that can't be done in the DB, it's easy to reformat the date/times as you extract the data, because it's being stored in a way the DB understands.