This depends upon what you are cooking! If you are cooking a Boston butt roast, it may take 30 minutes. If you are cooking baby back ribs, it may take 10-15 minutes. The purpose of the parboil is to...
Clean the spuds and cover them with water in a pan. Boil them for about 5 minutes. After that, drain the water and slit the spuds and wrap them in foil (optional) and finish them off on the grill or...
You are talking about blanching, and it doesn't take long, depending on the type of tomato, usually about 30-60 seconds. Try one or two to get a "feel" for it.
To be honest par-boiling potatoes is the same no matter what. Cover the potatoes in the pan with water and bring to the boil, then turn down until they are simmering. Leave for about 3-5 minutes but...