It really depends upon your experience, ability, and tools at your disposal. I would expect a couple of hours minimum if you have not done one before and if you do not screw anything up.

The timing marks should not move if you align them properly before you start. Take a look in the FAQs and see if you can find a decent tutorial on it and it will outline the timing marks. The factory manufacturer for your water pump is Aisin, if you have not bought one already I recommend either a factory Volvo pump or an Aisin. Your timing belt tensioner is a hydraulic one, becareful compressing it, if you compress it too fast you can damage it and subsequently damage your engine.

Mark