How many hands?

How many hands do I need on someone to begin to have accurate numbers for PFR% and flopseen%? I know short term these numbers can be high or low but how many hands does it take until they become somewhat accurate?

My SWAG.

After about 20 you make make a guess.
After about 50sih you get a clue.
Around 100 is enough to put people on pretty good pre-flop ranges.
As you approach 1kish things really become clear.