Why can't I modify dates individually?

I booked a client for drop in visits today and she needed 1 drop in visit on one day and the next day she needed 2 drop in visits and the following day she just needed the 1 visit again. It won't let me modify the days individually making it where I have to put 2 drop in visits for all 3 days when she only needs 4 total drop in visits but ended up charging her for 6 because I couldn't change the dates individually. I've hit edit and it will only let me do all 3 days together as 1 drop in visit a day or 2 drop in visits a day. I think the site needs to be updated to modify dates individually because drop in visits vary. This is a huge inconvenience because I don't want to overcharge my clients or underpay myself because there's no way to change it. Hope this helps! Thanks!