Have you noticed Time Machine giving you erroneous error messages? That it failed to backup, but it actually hasn’t? Well, this is not you. It’s a bug that is yet to be fixed as of this writing 10.5.6. If you get it simply go to the time machine icon next to the clock.
Then choose to “Back Up Now”. It should put everything in sync. In fact, make sure your Time Machine is working buy choosing “open time machine preferences…” You’ll then get a dialogue telling you when the last successful backup occurred.
Mine says it backed up Yesterday. (I’ve got it on a daily schedule instead of hourly). If you want to change the interval download Time Machine Editor to make adjustments. It’s FAH-FAH-FAH-FREE!