[php] Adding 30 minutes to time formatted as H:i in PHP

Having a nightmare at the moment and just can't see why it isn't working

I have a value in the form H:i (ie 10:00, 13:30) etc called $time

What I want to do is create two new values, $startTime which is 30 mins before $time and $endTime which is 30 mins after $time

I have tried the following but just doesn't seem to want to work

$startTime = date("H:i",strtotime('-30 minutes',$time));
$endTime = date("H:i",strtotime('+30 minutes',$time));

If I pass through 10:00 as $time and echo out both $startTime and $endTime I get:

$startTime = 00:30
$startTime = 01:30        

$time = 30 * 60; //30 minutes
$start_time = date('Y-m-d h:i:s', time() - $time);
$end_time = date('Y-m-d h:i:s', time() + $time);

In order for that to work $time has to be a timestamp. You cannot pass in "10:00" or something like $time = date('H:i', '10:00'); which is what you seem to do, because then I get 0:30 and 1:30 as results too.

Try

$time = strtotime('10:00');

As an alternative, consider using DateTime (the below requires PHP 5.3 though):

$dt = DateTime::createFromFormat('H:i', '10:00'); // create today 10 o'clock
$dt->sub(new DateInterval('PT30M'));              // substract 30 minutes
echo $dt->format('H:i');                          // echo modified time
$dt->add(new DateInterval('PT1H'));               // add 1 hour
echo $dt->format('H:i');                          // echo modified time

or procedural if you don't like OOP

$dateTime = date_create_from_format('H:i', '10:00');
date_sub($dateTime, date_interval_create_from_date_string('30 minutes'));
echo date_format($dateTime, 'H:i');
date_add($dateTime, date_interval_create_from_date_string('1 hour'));
echo date_format($dateTime, 'H:i');

I usually take a slightly different track to achieve this:

$startTime = date("H:i",time() - 1800);
$endTime = date("H:i",time() + 1800);

Where 1800 seconds = 30 minutes.

Just to expand on previous answers, a function to do this could work like this (changing the time and interval formats however you like them according to this for function.date, and this for DateInterval):

// Return adjusted start and end times as an array.

function expandTimeByMinutes( $time, $beforeMinutes, $afterMinutes ) {

    $time = DateTime::createFromFormat( 'H:i', $time );
    $time->sub( new DateInterval( 'PT' . ( (integer) $beforeMinutes ) . 'M' ) );
    $startTime = $time->format( 'H:i' );
    $time->add( new DateInterval( 'PT' . ( (integer) $beforeMinutes + (integer) $afterMinutes ) . 'M' ) );
    $endTime = $time->format( 'H:i' );

    return [
        'startTime' => $startTime,
        'endTime'   => $endTime,
    ];
}

$adjustedStartEndTime = expandTimeByMinutes( '10:00', 30, 30 );

echo '<h1>Adjusted Start Time: ' . $adjustedStartEndTime['startTime'] . '</h1>' . PHP_EOL . PHP_EOL;
echo '<h1>Adjusted End Time: '   . $adjustedStartEndTime['endTime']   . '</h1>' . PHP_EOL . PHP_EOL;

Your current solution does not work because $time is a string - it needs to be a Unix timestamp. You can do this instead:

$unix_time = strtotime('January 1 2010 '.$time); // create a unix timestamp
$startTime date( "H:i", strtotime('-30 minutes', $unix_time) );
$endTime date( "H:i", strtotime('+30 minutes', $unix_time) );

What you need is a datetime which is 30 minutes later than your given datetime, and a datetime which is 30 minutes before a given datetime. In other words, you need a future datetime and a past datetime. Hence, classes that achieve that are called Future and Past. What data do they need to calculate what you need? Apparently, they must have a datetime relative to which to count those 30 minutes, and an interval itself -- 30 minutes in your case. Thus, the desired datetime looks like the following:

use Meringue\ISO8601DateTime\FromCustomFormat as DateTimeCreatedFromCustomFormat;

(new Future(
    new DateTimeCreatedFromCustomFormat('H:i', '10:00'),
    new NMinutes(30)
))
    ->value();

If you want to format it somehow, you can do:

use Meringue\ISO8601DateTime\FromCustomFormat as DateTimeCreatedFromCustomFormat;

(new ISO8601Formatted(
    new Future(
        new DateTimeCreatedFromCustomFormat('H:i', '10:00'),
        new NMinutes(30)
    ),
    'H:i'
))
    ->value();

It's more verbose, but I guess it's way less cryptic than built-in php functions.

If you liked this approach, you can learn some more about the meringue library used in this example, and the overall approach.

echo date( "Y-m-d H:i:s", strtotime("2016-10-10 15:00:00")+(60*30) );//2016-10-10 15:30:00

or

echo date( "H:i:s", strtotime("15:00:00")+(60*30) ); // 15:30:00

or

echo date( "H:i:s", strtotime(date("H:i:s"))+(60*30) ); // 15:30:00