The mechanic says that he is going to "go home to see Esther" his wife. It can be assumed that the shop is closing for the day, and since this is the day of Michelle's birthday party, it is likely either a Saturday or Sunday, in which shops routinely close early. What prompted the mechanic to come back to the shop 3 hours later? Unless this shop closes for a while during the middle of the day (which is not likely since the time of day was already afternoon), it doesn't make any sense that the mechanic would have had any reason to come back to the shop. In the 90's cell phones were not prevalent, and Jesse wouldn't have known how to get a hold of the mechanic at home to ask to be let out.