generate times by half hour increments

displaytime.php

<?php

// This should replace the DisplayPracticeTimes function.

$startTime = strtotime('08:00');
$endTime = strtotime('21:00');
$increment = 30 * 60; // 30 minutes in seconds

$times = array();

$current = $startTime;
while ($current <= $endTime) {
    $time = date('H:i', $current);
    $times[] = $time;
    $current += $increment;
}