you can easily do something like that.
Let's say you have an entity "booking", with a date as attribute, link to another entity "doctor".
association will be : one doctor can have several booking.
Now you simply need to do a retrieve in your microflow of every booking where the association of booking-doctor = the doctor selected by the current user.
then you filter on the date to be equal current day. Then a count of the filtered object. If >10 you display an error message.