my doctor doesn't check at all until you're at the hospital in labor. i did ask her to check when i was there for my gbs test though, since i was already half naked on the table.
it really doesn't matter though, you could have no progress and give birth a few days later, or you could be 2cm and give birth 4 weeks later. it's frustrating either way because if you're not dilated you'll be upset that nothing's happening, and if you are you'll be waiting and waiting thinking it could be any day.