I'm with Ladidah and Eggplant. Of course, I'm an old fart, but I do 16 miles one way and started out on my 63rd birthday allowing 2 hours, just so I'd have a margin. My best time yet is 63 minutes, but I still allow 90, so that I have time to change clothes and decompress (or fix a flat, or admire a wildflower, or get sidetracked some other way). I keep thinking I'm going to pour it on and decrease my time significantly, but a goodly portion of the reason I commute is to have time to reflect and cool it, and I'm damned if I'm going to make it some kind of performance exercise (except once in a while, just for the fun of it.)