I'm not a shabby mechanic myself, I'm no near good, but I can get things fixed and do a decent job at it.
I've torn my top end apart once just to inspect, and it took me a good 3 hours I'd guess to get it done, I'm assuming it took a little longer since it was my first time.
A good chunk of that time was spent coaxing the cylinder off.
To be honest, with my bike at least, I don't see why there would be any problem with leaving the head on when changing the rings.