Need to iterate through DateTime appointments with multiple bookings - php

Question

I have a MySql Database with peoples' names as varchars and appointment times as DateTime objects. I need to make a function that returns the next available time slot (DateTime format) found in the database, I'll use it to schedule people for that time slot.
Appointments are only on Tuesdays and Wednesdays. Whether it's Tuesday or Wednesday, 4 people can be seen at 9:00am, and 2 people can be seen at 10:30am.
This function returns the number of people that are booked for a given time slot (DateTime).
function getTimeSlotCount($dateTime)
{
// finds out how many people are scheduled for the given datetime
global $db;
$query = "SELECT * FROM appointments
WHERE AppointmentTime = :dateTime
ORDER BY AppointmentTime";
$statement = $db->prepare($query);
$statement->bindValue(':dateTime', $dateTime);
$statement->execute();
$count = $statement->rowCount();
$statement->closeCursor();
#var_dump($count);
return $count;
}
I plan to use a do while loop to iterate through timeslots. But I don't know how to iterate through appointment times that I mentioned using DateTime. Also how to compare the time portion of a datetime to a specific time of day?
function getNextAvailableTimeSlot()
{
$maxFor9am = 4;
$maxFor1030am = 2;
$isAvailableSlotFound = false;
do {
// How Do I: Assign next Timeslot to $AppointmentTime;
$numBooked = getTimeSlotCount($AppointmentTime)
if ($numBooked >= $maxFor9am && $HowdoIGetTimeFromAppointmentTime == 9am)
continue;
else if ($numBooked >= 2 && $HowdoIGetTimeFromAppointmentTime == 1030am)
continue;
else
$isAvailableSlotFound == true;
} while ($isAvailableSlotFound == false);
return $AppointmentTime;
}
EDIT: When an appointment is added to the database table. The person's name and a DateTime is entered for the record of the appointment.