they took 2 days to fix mine (from the Time UPS came to pick it up to when i got it back in the morning 2 days later), thats about the time it takes.
of course if you sent it you should have a UPS tracking number that you can input into the web site and they give you the tracking. Then in the apple site you can find the repair status.
Hope it helps
In most cases they do not "fix" your original phone, but rather send you a refurbished equivilent. Therefore, it only takes processing and transport time (and, if its a warranty repair, I assume they also determine whether the problem was caused by the user--such as a broken screen--or is a product defect).