The problem is, at higher lvl you'll need a LOT of time to play, since high lvl instances sometimes require 40 ppl - organizing that takes a couple of hours
Dungeons are huge and take a lot of time to complete, and you can't simply leave your group in the middle of the instance, right before fighting the main boss... So be prepared for that if you buy this game, weekends are gone
Battlegrounds may take hours, too, I don't even enter them on weekdays anymore.
At higher lvls you can't really do anything alone (it's not fun) so the time you spend with playing will be affected be other players'/friends' playing customs too.