Or just maybe...if we think logically of other explainations. All reservations in one category are the same "time blocks" so an appointment to acquire will take a carry timeslot.
I saw a just-canceled appointment for today very early this morning. So, I left it alone and checked all the other categories.
True that the length of appointments vary from 10 to 30 minutes, but at least all the 10 minute appointments should be able to use the same time if the scheduling periods are "pooled".
Both PTA and Registration appointments for 3 guns or less are 10 minutes in length. While I saw a PTA available, no Registrations were. That proves that the entire system is not using a single pool of appointments.
Could the registration and permit appointment have 2 separate pools since they are two different locations at HPD? Potentially.
The issue I see is that with 10, 20, & 30 minute appointment periods for different categories, the overlap would be unmanageable. Unless the larger appointments are booked first, the smaller ones would fragment the time pool, making it difficult to find contiguous segments to schedule larger periods.
Example: If 1:00-1:30 is open, and someone schedules a 1:10 3 or less PTA, the time between 1:00 and 1:10 can only be used for another 10 minute appointment. Likewise, a 30 minute appointment won't fit from 1:10 to 1:30. I can't see them using a simple pool of times when the length of individual appointments vary by 10 or 20 minutes. It severely complicates the process.
Given the number of windows at the permit desk, I can assume they anticipated multiple customers, telling me the reservations for each category overlap.