How can I substract 15 min from a start-time? - php

Question

I tried to substract 15 min. from another time (start-time).
I want to check if the current time is 15 min. befor a meeting starts.
foreach($result->value as & $value) {
$start = $value->Start->DateTime;
$startmeeting = substr($start, 11, -11); //cut time to hour:minute
$now= date('H:i', time());
$min= strtotime('-15 minutes');
$timebefor = date($startmeeting, $min); //Here I want to substract starttime with 15 min
if( $now >= $timebefor && $now <= $startmeeting )
{
//Show yellow warning box
}
}
Is it even possible on this way?

Answer 1

You basically have your solution, but it is untidy, and contains bugs. I think you want to do something like this:
foreach ($result->value as $value) {
$meetingStart = strtotime($value->Start->DateTime);
if (($meetingStart > time()) &&
($meetingStart < strtotime('15 minutes')))
{
//Show yellow warning box
}
}
Simply put: If the meeting is in the future, but less than 15 minutes into the future, you will have to show the yellow warning box.
When programming always pay attention to the names you choose. Notice how I use $nowPlus15Minutes which does clearly indicate what that variable contains. You used $min which isn't very self explanatory. The same problem exists with names like $value and $start. Perhaps $timebefor is a misspelling?

Answer 2

I recommend that you use PHP:DateTime with this. If your system works with external API (such as Google Calendar), I will usually specify the timezone too.
$currentTime = new DateTime("now", new DateTimeZone("Asia/Singapore"));
$reminderTime = new DateTime("2019-08-08T12:00:00.0000000", new DateTimeZone("Asia/Singapore"));
$reminderTime->sub(new DateInterval("PT15M")); // PT means period time, 15 minutes.
// Comparison of DateTime is allowed from PHP 5.2.2 onwards
if($currentTime > $reminderTime) {
// Do something
}
// For DEBUGGING
echo $currentTime->format('Y-m-d H:i:s') . "\n" . $reminderTime->format('Y-m-d
H:i:s');
Refer to DateTime documentation for more information.