There is a lot to consider. The thickness, type of meat and volume of water are going to make a large difference between items and time. The most important thing is you reheat the food to a safe temperature and then worry about quality. What I mean is you'd rather over do it when reheating as you are getting used to it.
I seal up my pork very flat & wide so it reheats faster. The other day I did have an issue with some brisket slices. Normally I make sure each slice is flat and not on top of one another. Well one end of the slices got on top of another and I did my normal brisket method, pull them out, and although the top ends of the slices were perfect, the bottom was still partially frozen in the center.
For pulled pork I prefer to boil a large pot of water, drop the bag in, turn to low & place a lid on. For 1 lb & under flat bags ten minutes usually works for me. Thicker bags go 15.