I was wondering how long it exactly takes to cook ground meat in a skillet on the stove on medium heat for these meats?  1) pork 2) bison  3) beef 4) chicken 
Because we don't know how hot your skillet is, how much ground meat you use and in which form the meat comes (as a thick patty or loose), you will have to use thermometer. The safe temperature of chicken and pork is the same like the safe internal temperature since there are bacterica inside the piece of meat and the suggested temperature already regards this.  Pork: 150 F or 66° C Chicken: 170 F or 76°C Beef and probably bison, too: 170°C or 76°C  If you want to cook loose ground meat (and measuring the internal temperature is difficult), cook it until the meat is not red/pink anymore. 