Hey guys,
Sorry, I've been away... haven't checked SDN in a while. Cammy and ygreenst answered the library-based thesis question pretty well. I did a lab-based one. It usually takes a little longer to do a lab-based one, because you have to run all the experiments, etc (unless you're doing some sort of statistical analysis of previously generated data- that counts as a lab thesis too). The upside is that it doesn't have to be any minimum length in terms of pages, although experiments tend to involve a fair amount of troubleshooting, etc. and may be more of a hassle than writing a library-based thesis.
Almost everyone I know who did a lab-based thesis graduated the following May (i.e., a year after classes ended). So they definitely seem to take a little longer. But that's the lag year, anyway, and you need to find SOMETHING to occupy your time
If you find the right advisor or can get a position at another hospital, you can get a salary while you're working on your thesis (it's perfectly acceptable). Some may require you to do other work, and just work on your thesis in your spare time, but others may let you spend days just writing and reading journal articles. Cammy is right, as usual: you need to sort of gauge the advisor and choose wisely.
Don't sweat the thesis until second semester though. You'll have your hands full enough the first semester. Good luck!