Adding 1 hour to time variable

You can do like this

    echo date('Y-m-d H:i:s', strtotime('4 minute'));
    echo date('Y-m-d H:i:s', strtotime('6 hour'));
    echo date('Y-m-d H:i:s', strtotime('2 day'));

Worked for me..

$timestamp = strtotime('10:09') + 60*60;

$time = date('H:i', $timestamp);

echo $time;//11:09

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Explanation:

strtotime('10:09') creates a numerical timestamp in seconds, something like 1510450372. Simply add or remove the amount of seconds you need and use date() to convert it back into a human readable format.

$timestamp = strtotime('10:09') + 60*60; // 10:09 + 1 hour
$timestamp = strtotime('10:09') + 60*60*2; // 10:09 + 2 hours
$timestamp = strtotime('10:09') - 60*60; // 10:09 - 1 hour

time() also creates a numerical timestamp but for right now. You can use it in the same way.

$timestamp = time() + 60*60; // now + 1 hour

$time = '10:09';
$timestamp = strtotime($time);
$timestamp_one_hour_later = $timestamp + 3600; // 3600 sec. = 1 hour

// Formats the timestamp to HH:MM => outputs 11:09.
echo strftime('%H:%M', $timestamp_one_hour_later);
// As crolpa suggested, you can also do
// echo date('H:i', $timestamp_one_hour_later);

Check PHP manual for strtotime(), strftime() and date() for details.

BTW, in your initial code, you need to add some quotes otherwise you will get PHP syntax errors:

$time = 10:09; // wrong syntax
$time = '10:09'; // syntax OK

$time = date(H:i, strtotime('+1 hour')); // wrong syntax
$time = date('H:i', strtotime('+1 hour')); // syntax OK