I'm planning to start doing a 20-22 one way commute. It's reasonably flat, and primarily downhill on the way to work; the last 3 miles will be on an MUP that goes right by the hospital.
I agree about the time issue, but in my mind, that will be partially offset by combining commuting with training, rather than coming home and going for a ride. I'm planning to do some MTB races this summer, as well as cx again in the fall, so I'm looking at this as a good way to get base miles in, with the option to extend the ride home and/or use it for intervals.
When I used to commute in the 90s, I had a 5 mile one-way. One of my neighbors worked at the same hospital. I could usually beat her home on the bike.