I just use the one, although that makes it a bit more time consuming working out hours breakdowns if you need to do so for a resume or whatever.
If I was smarter and more forward thinking I would have kept a spreadsheet or something with every conceivable permutation of hours, but I'm not, so every time I need to fill in a form with some whacky hours sub-total it's back to the log books, calculator and head scratching...