I go to the bathroom before I leave for the gym or as soon as I get there. I stay at a station until I'm done using it (unless I have to give someone a spot, or go to the water fountain -- either of which take about 30 seconds). I have a towel with me, my notebook and my half-gallon jug with my intra-workout concoction in it.
3 minutes is enough time that it's up for grabs as far as I'm concerned. Where I work out, people don't put their weights away and that's always my excuse if I "take" someone's station. I can't tell the difference. If I didn't see you on it within a minute or two before, or if you've vacated it for long enough (to go to the bathroom, go text someone, or jumping to another machine like Tim mentioned), it's fair game.
That's why, as far as I'm concerned, if you want to circuit train like that, you go to the gym at an obscure hour when it's empty. Back in the day, when I would utilize superset training, I'd go early in the morning when there was maybe one other person in there, so I knew I could do that. Even then, I was still done with the 3 or 4 stations I was using in a total of no more than 10 minutes.
No one is going to wait on you if you give them an opening and I'm sure not waiting on someone else unless they're actually using the machine.