ooh, something I really know about! How exciting.
I replaced the timing chain on my '83 240D over labor day weekend. Also replaced the camshaft sprocket, idler gear, upper slide rail, and tensioner. Also replaced all the belts and hoses (incl. coolant flush & fill), and a brake caliper and some other minor things, like refurbishing my dome light and replacing a headlamp. All this was done in 2 days with some help from my dad. I would have liked to also replace the tensioner rail, but could not get the bearing pin out for that rail. :/
First of all, the timing chain alone isn't very hard at all. The only special tool you really need is the chain press crimping tool to press the last link in. Other tools that are quite handy are a dremel tool (to grind open old chain) and some allen wrench sockets that fit on a ratcheting socket wrench. The more parts you replace/rebuild, the more time the job will take. (well, yeah)
You have to pull the radiator out to get at the timing chain properly, and if you're pulling out the tensioner you also have to take the thermostat off. I found this to be an excellent time to change all the hoses, since half of them were off and the coolant was drained anyway. I should have also replaced the thermostat, but didn't think about it.
If you're replacing the tensioner rail (or at least attempting to, like me) then all the belts have to come off, which means it's a great time to put new belts on. Also, the main pulley is attached by six bolts that take a 6mm allen wrench. It's nigh-impossible to actually take these out with an allen wrench; save the time and frustration and pick up some allen-wrench sockets to fit your socket wrench.
The timing chain gears don't necessarily HAVE to be replaced, but I bought a whole kit that included them, so I went ahead and replaced them. They were showing a little bit of wear.. not so much that I was concerned about it, but a little bit.
Also, while you're in there, it's a good time to do a valve adjustment, if you haven't had one done in the past 5k or more miles. Generally you shouldn't need a valve adjustment any sooner than 10-15k miles, but if you've got the valve cover off anyway, why not? If you've got the right wrenches and feeler gauges, it only takes half an hour or so.
If you're a great mechanic and have all the right tools, you could probably do all this in a day. If you're replacing more stuff or need to stop to go buy tools, expect it to take 2 days, depending on how much you do.
'83 240D, 250k miles