How to estimate how long a tournament is going to last

Hi

Im planning to organise a NL Texas holdem tourney with friends. I think we'll be 15-20 ppl, and I would like for it to last 4-5 hours.

Is there some sort of formula to raise blind levels I can use to approximate the time I want to acchieve?

I've tried looking for it on google but haven't really found a good answer.

Hmmm...I found the following on Google without much sweat.

How to Set Up a Poker Blinds Schedule

Thank you!!