When going anywhere by bike, I find that if I know the distance, I can usually predict my time to the minute. I use the 15 mph rule. If you average 15mph, you are covering a mile every 4 minutes. So just multiply your distance in miles by 4 to get the number of minutes it will take.
exactly: and the converse - i know how far things are. i was talking to a coworker at lunch and about where we live and i said i live about 10km direct or 11km from work and said, yeah, me too! then we found out he lives about twice as close to work... his DRIVE is 11km, although the real distance is about 6km.
most people have a really warped sense of how far or close things are - if it's near the interstate or freeway, then it's "close" even if it's 30 miles away... and a few blocks through the neighborhood is "really far"