<?php
$array = [
'2020-02-07' => ['09:00' => 1500, '10:30' => 1500, '11:00' => 1500, '11:30' => 0],
'2020-02-08' => ['09:00' => 1500, '09:30' => 1500, '11:00' => 1500],
];
$result = [];
$f = fn($p) => date('H:i', $p);
foreach ($array as $k => $v)
{
$v = array_map(fn($a) => strtotime($a), array_keys($v));
for ($i = 0; $i < count($v); $i++) {
[$a, $b] = [$v[$i], &$a];
while (isset($v[$i + 1]) && $v[$i + 1] - $v[$i] === 1800) [$b = $v[$i + 1], $i++];
$result[] = ['date' => $k, 'range' => $a == $b ? $f($a) : $f($a) .' - '. $f($b)];
}
}
print_r($result);
preferences:
76.46 ms | 402 KiB | 5 Q