This is why I don't post on these boards as much as I'd like to: threads like these. Your assuming that everyone is leaving for the same reason, that your opinion of what time to leave and come back is right. Your not looking at the whole picture and the context in why people are leaving. Yesterday, I went to football with my grandad who understandably isn't as fit or strong as he used to be. We go down 5 mind early before half time so he can go down the steps easily. We leave early because he's cold, and wants to beat the crowd of people. How is this a bad thing?
What about people that work? People that need to be somewhere? People in my situation? With kids? With people at home they need to be with? People that come to the football as a day out with friends rather than solely for the football? The people that have paid £20+ to these players ridiculous wages and don't want to watch 5 mins of scrappy football at the end so they can get back to their families and have dinner?
Have some common sense and remember that you aren't the 'perfect supporter' and you have no idea about other people...