Often when the Internet connection goes down for a "quitter", he does not notice it immediately and sit there staring at "Loading" having no idea he is dicoed until the game pops up a message (if it does). At this time, more than one minute has passed. Then it is usually a good idea to restart your browser before connecting again. I think 3 minutes is not unrealistic for that and if it goes faster, well, then they are in quicker.
I remember my old Dell laptop, Windows XP, that I had until a year ago. If it crashed it took close to 5 minutes to get it ready for action.
So no, I think 5 minutes is reasonable :)
It is very impolite though when people just close their browser and quit without intending to reconnect, forcing the opponent to sit there for 5 minutes. Should go into the stats. Maybe a "Being an Ass" award. If you see someone has a Crystal, you kindly reject the invitation :)