It depends on what else you are doing. If you shut all the apps on your Mac or let it go to sleep, the battery will be fully restored faster.
If you are working on your Mac at a reasonably constant rate, then the figure will be accurate. Cut down the intensity of what you are doing and it will go down, start burning lots of CDs to the hard drive and it may go up. Just like how fast the battery power goes down.
It might be worth recalibrating your battery though if you haven't done so recently. Take it to full charge and then unplug and use until the PB puts itself to sleep when it gets down to less than 5%. Then plug it in and allow it to charge back to full again.