Get seconds difference from current time to given time. Will always compare closest time.

diffTo.php

<?php 

function diffTo($toTime)
{
    $now = strtotime('now');
    $next = strtotime('today ' . $toTime);

    if($next <= $now){
      $next = strtotime('tomorrow ' . $toTime);
    }

    return $next - $now;
}

// example
$nextTime = '13.19';

echo 'current time is ' . date('Y-m-d H:i:s');
echo '<br/>';
echo 'next time is ' . $nextTime;
echo '<br/>';
echo 'diff to next time in minutes: ' . round(diffTo($nextTime) / 60, 2);