I'm planning to cook my 4lbs pork in the oven but as my guests arrive at 1pm for lunch, I wanted to start the cooking the evening before and then keep the partly cooked pork in the fridge till next day and finish up the cooking then. Would that make the pulled pork tender and tastefull and what about safety? Alternatively, could I set the oven temperature very low and cook the pork all night for a 1pm finish? Thanks!
You can completely cook it the night before. Pulled pork will reheat quite well.
Alternately, you can cook it completely that morning, and hold it for an hour or so before your guests arrive. It should braise or roast in no more than 3-4 hours, tops, which should allow you to cook it the same day. You can then hold it a while for service, if you don't want to be pulling in front of your guests (I would; its fun). It should have enough mass that in a covered container, maybe with a towel over it as a blanket, that it won't cool off too much.
Home ovens don't hold temperatures terribly accurately, especially at the low end of their ranges, so I would not try some sort of overnight cooking.