Probably an hour or two in most places, but it depends. Was in Portland the other night, and this is about what I recall...
Casa Diablo - 45 minutes (stayed long enough to see most of the lineup and decide whether it was worth getting dances from the dancer hanging off me and groping. Would go back.)
Club Rouge - 30 minutes (second club and second dancer cock-blocking. shook her off but left after one of the dancers who caught my eye onstage sounded really nasally like she had a cold - fallback club because that annoying valley girl voice was offset by a phenomenal ass and perky tits)
Luck Devil Lounge - 5 minutes (Ashton was a hot little number, but walked out to the smoking deck to her regulars after being onstage and nothing else seemed worth staying for)
Safari Show Club - 30 minutes (got dances from Jameson, kinda like a deep tissue massage with a hot naked stripper grinding on your lap. Not typically what I look for, but was nice since I had a crook in my neck - stayed a little longer to watch Vegas shake her ass on stage)
Rose City Strip - 45 minutes (stage dances were pretty decent with some tip rail grind. Cory could have gotten dances but decided to hang out with bikers. Dagger was hot but full of herself and seemingly low mileage. Saw a blonde and short-haired brunette who looked interesting. The brunette freed up first. Jordan. Not the greatest mileage but 3/100 full nude dances were worth it. Would go back.)
Hawthorne Strip - 5 minutes (Forgot the dancer's name who was onstage. Only one of two dancers I saw. Dark hair and big tits. Curvy but not fat. She was paying a lot of attention to the other guy tipping, and it was getting late enough where I cut bait quickly. With more time I might've tried her out. Waved at the bartender staring at me walking out.)
DV8 - 5 minutes (Same deal here. Wanted to check out Club 205 and the skinny dancer on stage was making her way around in the wrong direction. Left a couple bucks and bolted.)
Special mention - Club 205 and Club Mystic advertise they close at 2:30 but the outside entry doors were locked by 2:05. A lot of clubs will let customers in right up until close if they might get dances, but in Portland not sure that's happening.
Portland club crawl - 7 clubs and about 165 minutes inside total.
165 minutes/7 clubs = 23.6 average minutes per visit