<?php declare(strict_types=1);

use Sunfox\DateUtils\DateTime;
use Sunfox\DateUtils\DateIntervalFactory;

$start = new DateTime('2015-01-01');
$end = new DateTime('2015-12-31');

$months = DateIntervalFactory::create($start, $end, DateIntervalFactory::MONTH, 1, [
	'incomes' => [],
	'expenses' => [],
]);

foreach ($months as $k => $month) {
	echo "{$k}: " . $month->date->format('Y-m-d') . PHP_EOL;
}

<?php declare(strict_types=1);

use Sunfox\DateUtils\SpentTime;

$spentTime = new SpentTime('1h30m');

echo (string) $spentTime; // 01:30:00
echo $spentTime->getTotalHours(); // 1,5
echo $spentTime->getTotalMinutes(); // 90
echo $spentTime->getTotalSeconds(); // 5400