display number of affirmed appointments in time slot

Hi there,
I would like to customize my appointments+ plugin in the way, that there is some kind of feedback in a time slot of how many clients have already an affirmed appointment in this slot.
There can be more than one clients at the same time (for now its 10, but this number can change), and I would like to give them a clue of how many are already registered for this time - for example by showing them the number of approved appointments within the slot.
do you have an idea how to put this into practice, is there a way to set up a counter and display its output?
the screenshot without numbers is as it looks now and with the numbers is one idea of how to give a feedback.
TIA!
Damaris