I mash for 60. But the # of grain that I do mash is minimal and it doesnt really effect my og to much. it does a little but not much. I have found with 60 I get the full amount of taste and aroma from the grain that I was looking for.
60 minutes is the starting point whether you're brewing PM or AG. The time and temp depends on how fermentable you want your wort. When I was PM'ing, I would mash for more fermentable wort to balance out the unfermentability of extract. So I'd recommend mashing for 60 minutes @ 150-152F...