Have big potential to be very good plugin, but its not yet there

I have services with 30min/60min/90min. when I put just one service 30min everything works very nice no problems, when I add 60min shit starts to happen. I book 60min, press book more to add another reservation and it shows not 60booked before, but 90, so I lose 30min for nothing, just idle , how bussines should work like that? and plugin creators add so much addons for multiple bookings but a lot of them do practicaly the same thing, so look very carefull what add on you buy, because you can waste your money…