In Security we raided 4 times a week, total of 16 hours. I can't remember us coming in on an off night to do progression, but occasionally we'd stay late if we were close to a kill on a new boss.
That said, in a lot of top-tier guilds 5+ days or extra hours a night is not unheard of during hardcore progression when a new tier is released until everything is on farm. However, once everything is on farm those same guilds do 2 or fewer nights a week since they don't need longer than that to clear everything. That's pretty much what we did during ICC when it was on farm - we'd clear the whole instance in a night and the rest of the week was either alt runs, older content (which is how I got my Mimiron's Head
), or sometimes PvP.