There is no exact formula because there are too many variables in play. It's not like there is a cutoff for the amount of research you do. Quality matters, whether or not you get published matters, your LORs matters. All these things may open the door to an interview, how you perform during the interview matters as well.
If you are going to be attending a post-bacc program for two years, why not do research during that time as well? If anything, the research experience will just open more doors for you assuming you maintain high grades and get a great MCAT score.