It's a fairly straight forward process, kind of. As long as the bolts don't break off from corrosion, and the stuff attached to the t-stat housing (vacuum lines) doesn't get in the way (just disconnect if necessary for the change) its pretty easy.
I siphon coolant out of the radiator with small vacuum hose (snake it down to base of radiator or as far as it will go) into a suitable container, if it doesn't need changing, so I can re-use it. When you do this, you don't have to worry about air bubbles in the system when refilling as much, nor do you have to remove as much coolant...just enough to get coolant level below the thermostat housing on the block. There will be some spill out anyways, but not so much. Pull off the fill neck end of the radiator hose, and move it out of the way.
Just need a gasket and the t-stat, and thats about it. Unbolt the housing, pull out the old t-stat, clean the mating surfaces up if necessary, and bolt it back together. I use silicone on the gasket all the time, but most of the time, its probably not necessary. (please no comments on silicone here...my vehicles haven't complained for the last 8 years about my practice) Silicone is one of those "works for some, not others" deal, so if you want to use it, and know how (very thin, not even a bead) go for it, if not, or you don't want to, don't. No biggie, whatever works and doesn't leak.
I would imagine, about a 30 minute job, cleaning up the surfaces, draining/refilling coolant, moving any stuff thats in the way. if a bolt breaks, its going to be considerably longer. As long as you don't burn yourself, it probably can't hurt to try and take the bolts out right after you get done driving it while its still warm...aluminum intakes are even worse by easily stripping threads, so keep that in mind if AL intake.
