Anyway, it really depends on how good of a dunger you are. It takes over a month of pretty much 6+ hours a day to get 99 dungeoneering from 1. Assuming your exp averages to about 50k per hour (Including the exp gained from level 1 and C1s). It would be around 250 hours for 99 alone. Faster or slower depending on who you dung with, or if you're a good keyer that can get floors done within 30 minutes.
For 120, no one can really give you an estimate. But the exp varies and you could get 200-400k exp per hour at 105+ dung. So a few more hundred hours.