I ride 24.9 each way. is your 17.5 one way or each way? I'll second 10 Wheels advice, ride it on a day off. You'll be hard pressed to ride 17.5 each way every day at first unless you're in good shape, but hit it a couple days a week and work up to it. It's certainly doable. Time depends on what bike you're riding as efficiency is the key here, but no reason it can't be done in 1:00 - 1:15 or so depending on terrain, your condition, and what you're riding.

-R