Depends, if you are leaving Chicago you can take the bus to Garfield in about 15 minutes. From there you can get on the green line and take that to the loop. If it is a rush period, the purple line can take you most of the way to Davis Street (closest stop to NU) without stopping. (I think Davis is like..the 6th stop from the loop if the purple line is running express. If the purple line is not running express.. well.. hop on the red line and take a nap. I took the train two days ago, non express, and I think it took roughly 2 hours and 20minutes.