- var_dump: documentation ( source)
- date: documentation ( source)
<?php
$starttime = ['month' => 5, 'day' => 10, 'minute' => 15];
$date = new \DateTime();
$date->setDate($starttime['year'] ?? $date->format('Y'), $starttime['month'] ?? $date->format('m'), $starttime['day'] ?? $date->format('d'));
$date->setTime($starttime['hour'] ?? $date->format('H'), $starttime['minute'] ?? $date->format('i'));
var_dump($timestamp = $date->getTimestamp());
var_dump(date('Y-m-d H:i:s', $timestamp));