<?php
 
	//Array com os horarios que possam ser imprimidos
	$hora = array('13:55:40','13:56:40','13:58:41','13:59:40','14:01:00','14:02:00','14:04:40',
	'14:05:00','14:07:10','14:08:00','14:10:23', '14:11:23','14:13:39','14:14:23','14:16:39',
	'14:17:23','14:19:13','14:20:23','14:22:40', '14:21:23','14:25:07', '14:26:23', '14:55:40');
 
	//Intervalo que o usuario escolherá entre 3, 15, 30 ou 60
	$interval = 15;
 
	$val1 = $hora[0];
 
	print $val1;
 
	for ($i=0;$i<(count($hora)-1);$i++) {
 
		$val2 = $hora[$i+1];
 
		$datetime1 = new DateTime($val1);
		$datetime2 = new DateTime($val2);
 
		$intervalo = $datetime1->diff($datetime2);
 
		$result = $intervalo->format('%i');
 
		if($result == ($interval-1) || $result == ($interval)){
		     print ", ".$val2;
		     $val1 = $val2;
		}
 
	}

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