Date & Time

A timestamp in PHP is a numeric value in seconds between the current time and value as at 1st January, 1970 00:00:00 Greenwich Mean Time (GMT).

    $_SERVER['REQUEST_TIME'];
    

    $_SERVER['REQUEST_TIME_FLOAT']; 
    

time()

The Unix epoch (or Unix time or POSIX time or Unix timestamp) is the number of seconds that have elapsed since January 1, 1970 (midnight UTC/GMT), not counting leap seconds (in ISO 8601: 1970-01-01T00:00:00Z). Literally speaking the epoch is Unix time 0 (midnight 1/1/1970), but 'epoch' is often used as a synonym for Unix time. Some systems store epoch dates as a signed 32-bit integer, which might cause problems on January 19, 2038 (known as the Year 2038 problem or Y2038).

    time();
    

    strtotime("15 November 2018");
    

Reference:
• https://www.epochconverter.com/
• https://brainbell.com/php/generating-a-timestamp.html

date()

PHP date function is an in-built function that simplify working with date data types.

    date(output format, epoch);
    

The PHP date function is used to format a date or time into a human readable format. It can be used to display the date of article was published. record the last updated a data in a database.

    $today = date("F j, Y, g:i a");                 // March 10, 2001, 5:16 pm
    $today = date("m.d.y");                         // 03.10.01
    $today = date("j, n, Y");                       // 10, 3, 2001
    $today = date("Ymd");                           // 20010310
    $today = date('h-i-s, j-m-y, it is w Day');     // 05-16-18, 10-03-01, 1631 1618 6 Satpm01
    $today = date('\i\t \i\s \t\h\e jS \d\a\y.');   // it is the 10th day.
    $today = date("D M j G:i:s T Y");               // Sat Mar 10 17:16:18 MST 2001
    $today = date('H:m:s \m \i\s\ \m\o\n\t\h');     // 17:03:18 m is month
    $today = date("H:i:s");                         // 17:16:18
    $today = date("Y-m-d H:i:s");                   // 2001-03-10 17:16:18 (the MySQL DATETIME format)
    

Timezone

    $timezone = date_default_timezone_get();
    echo "The current server timezone is: " . $timezone;
    

    date_default_timezone_set('Australia/Melbourne');
    date_default_timezone_set('America/Los_Angeles');
    

DateTime()

    use \Datetime;
    
    $now = new DateTime();
    echo $now->format('Y-m-d H:i:s');    // MySQL datetime format
    echo $now->getTimestamp();           // Unix Timestamp -- Since PHP 5.3
    

Timezone

    $now = new DateTime(null, new DateTimeZone('America/New_York'));
    $now->setTimezone(new DateTimeZone('Europe/London'));    // Another way
    echo $now->getTimezone();
    

    $timezone_identifiers = DateTimeZone::listIdentifiers();
    foreach($timezone_identifiers as $key => $list){
        echo $list . "
";
    }
    

mktime()

    //mktime(hour, minute, second, month, day, year, is_dst);
    echo mktime(0,0,0,10,13,2025);
    

Parameters