As an old fat guy (49 & 260) I commuted 20 miles one way in 1:20 and did a one time commute of 28 miles (56 rt) in 1:59 and 2:16 on the way back. My normal exercise loop is only 9 miles with a 1 mile hill at the end and I do that in between 38-42 minutes. My fastest recent 10 mile ride was exactly 30 minutes over rolling terrain and no stop lights on a Long wheelbase recumbent. If you are younger, lighter and in better shape, with two good knees, your times should be better unless you have a bunch of stoplights to contend with.
Hope this gives you something to gauge your times with.