Unfortunately, the date does not exist in Pokemon Sapphire or Ruby - thus it cannot be changed. The time feature is also cemented from the very beginning, so you cannot change it either - even for Daylight Savings.
Alternatively, you can do what i did (be careful)! What i did, was look at the time in the game, note it, then the hard part. You have to get either a screwdriver to fit in the game cart, or a flat headed one. Once you unscrew it, slide the cover a bit, then lift. For me (not sure if it's the same for you) the metal thing touching the battery was not attached, i could just move it off gently. Sometimes, that's how the "internal battery has run dry" thing happens from the metal not touching the battery. So once you lift the metal part from contact to the battery, wait until your time matches with the one you noted. once it does, make it have contact again (this might be tricky, but don't worry, it's strong, bending it to make it have contact isn't a problem).