Monday 9/24 is the last day to drop without a “W” on your transcript. Parents are/were told at orientation that professors tend to lighten up during these 1st three weeks of September, because they know students are dropping, adding and swapping classes. So I don’t know if the “try it out” approach is the best approach.
Also, FYI, the UM tuition is exactly the same amount whether a student takes 12 units up to 18 units.