OK, from a GPs point of view....
We are very pressured to keep to time, and are only allocated 10 minutes per appointment slot- it would be great all round if it were more. I typically see 18-20 patients per session, so overrunning can be a bit unfair on patients with the later appointments. It will usually take 10 minutes to deal adequately with a problem, including arranging referrals and doing the paperwork. However, if someone has a couple of quick things that can be done within time, then that's fine and can be done easily. Of course, some consultations may take longer due to the subject matter, and that's also fine- I would never dream of chucking someone out because they had exceeded their 10 minute slot if they genuinely needed longer.
Can I suggest, that if you know in advance that you are going to need a long appointment, just book a double slot. It gives all of you more time and means you are far more likely to get your problems sorted properly than being rushed.
I must say that I have never enforced the one problem per appointment rule, but am seriously tempted as a lot of people really take the piss. I've had 4 members of one family all insist on being seen on one appointment, I've had people turn up with lists of 10 problems and more which they expect me to sort. I have only ever once asked a patient to come back another day to finish off her problem list, but it was after she'd had 45 minutes of my time already and none of the rest were urgent. Also, it would be great if people could start with the most important problem first, instead of leaving it to mention just as they are about to go out of the door!
Am I missing the stress of being a GP while I'm on maternity leave? No way!