For me, 1 week good, 2 weeks great, 3 weeks gone. No idea how one would be if it actually sat for a whole month. In general, I’d say 3 weeks or so at lager temps (based on how the last glass is usually the best).
Ah one (lick)… Ah two (lick)… Ah three (CRUNCH)… It takes three licks to get to the center of a [keg of beer] - The Owl from the old tootsie pop commercials
2-3 weeks depending on yeast flocculation, use of fining agent, how careful I was when racked it into the keg, and other such stuff.
One super-hoppy red ale (think a super-hoppy APA with 2 oz of Carafa II) was a cloudy mess for 3 weeks and then only cleared fully for the last couple pints.
I don’t even fine my APA/IPAs as it seems to remove some of the hop aroma when I do. I the case of the Biofine Clear it has totally stripped all hop aroma and flavor leaving a very bitter and clear but boring IPA.
For IPAs, the fresher the better for my tastes, after about 4-7 days cold crash to drop yeast.