Right now, record low interest rates have created a big backlog for re-fi's. 14-21 days has been a reasonable time frame to get an appraisal back. *Right now*, 21 days is about the shortest timeframe (if the buyer really hustles to get it ordered with a local lender, then you can get one back between 14-21 days).
Getting a financing contingency removed is trickier. It's typical to have these set at 28 days, however, these contingencies continue after the deadline, unless the buyer takes the action to remove it. The challenge for a buyer is that lenders will tell you that the loan is approved through underwriting, but they'll always have conditions tacked on -- like verification of employment and credit just before closing, etc. As a seller, to get any real protection from financing contingency contract language, you must complete a lot more due-diligence on the buyer's qualifications before you actually ratify.
That's a long answer, but I most sellers think that if they get past the number of days on financing, then they're home free. And that's simply not the case. The buyer can have ton's of exits out of a contract based on financing.
Hope that helps. Good luck.