I recognise some of what you wrote here... I had a hardware problem right from the start (as you probably saw a while back if you've been lurking for a while). I found SLRs incredibly painful around the kneecap and shooting upwards - my hardware was sticking into my muscle and they had to take it out very early. It could be that yours has shifted slightly, which might cause it to start hurting. Lostpirate's hardware shifted a month or so back too.
Go with prepared questions to the appointment tomorrow - ask for an x-ray if they don't come up with sensible reasons for your problems. I had to really push to get an x-ray as they didn't take me seriously at all (didn't want to admit there was a problem as it meant admitting their surgery hadn't been perfect). If the hardware is shifting you should be able to see it.
I have problems with my right knee too (broke the left one) as it had to take too much strain on its own. It still hurts now - sometimes more than the broken one. My physio has given me core-strengthening exercises (like pilates) to help me walk straight, which seems to be working well. They also have me walking backwards as much as possible - I had been limping/on crutches for so long that I'd forgotten how to walk straight forwards and was causing more problems. You don't walk backwards, so never learn to walk wrongly backwards - so your body kind of walks normally backwards then remembers how to do it forwards again! Sounds mad, but I found it hurt less walking backwards and I lost my awkward gait really quickly (10 days?).
As for how long it takes to recover from hardware removal... I had about a week or 2 off work so I could rest, but I had an arthroscopy on my right knee at the same time, so maybe you'll be quicker. It healed so much more quickly the second time and was nowhere near as painful - it's nowhere near as bad as the first surgery as the bone is healed and just has to fill the holes. Also your body isn't in shock in the same way. I was full weight bearing straight away, but needed crutches for a while. I'm only just off them (2 months later) but that was because of doing both knees - I reckon it'd have been half that with only one knee.