If there is a longner time limit such as 30 minutes per game it usually takes me 20
minutes to finish a game. At the chess club where clocks are optional games last about 40 minutes unless there are long endings. It appears that 20 minutes is an optimal time for most games. If there is a position with a difficult decision it doesn't take too long to decide that there are no preferences of choice. Other criteria may come into play such as whether to end with a knight or a bishop.
what is your usual time limit you put on the clocks when you play chess that you feel most comfortable with and gives you enough time to think with out feeling rushed? Generally i prefer to have about 10 - 15 minutes which i usually more than enough which gives me extra time incase if im playing with someone around the same skill level as me and the match appears to be going nowhere.