I haven't dealt with time stuff in SQL recently.I believe all of the time functions (in perl) give you an epoch number (seconds since January 1, 1970). So make sure that the comparison that you are using in your SQL table is comparable. If not you may need to format your epoch time to look like the one in your SQL table.

Also, I don't think you need to necessarily do a prepare/execute combo when just deleting something. If you wanted you could just use a $dbh->do(statement)

Hope this helps