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</span>
$today = date ( "j, n, Y" );
// 10, 3, 2001
$today = date("Ymd");
// 20010310
$today = date('h-i-s, j-m-y, it is w Day');
// 05-16-18, 10-03-01, 1631 1618 6 Satpm01
<span class="token variable">$today</span> <span class="token operator">=</span> <span class="token function">date</span><span class="token punctuation">(</span><span class="token string single-quoted-string">'it is the jS day.'</span><span class="token punctuation">)</span><span class="token punctuation">;</span>   <span class="token comment">// it is the 10th day.</span>
<span class="token variable">$today</span> <span class="token operator">=</span> <span class="token function">date</span><span class="token punctuation">(</span><span class="token string double-quoted-string">"D M j G:i:s T Y"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>               <span class="token comment">// Sat Mar 10 17:16:18 MST 2001</span>
<span class="token variable">$today</span> <span class="token operator">=</span> <span class="token function">date</span><span class="token punctuation">(</span><span class="token string single-quoted-string">'H:m:s m is month'</span><span class="token punctuation">)</span><span class="token punctuation">;</span>     <span class="token comment">// 17:03:18 m is month</span>
<span class="token variable">$today</span> <span class="token operator">=</span> <span class="token function">date</span><span class="token punctuation">(</span><span class="token string double-quoted-string">"H:i:s"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>                         <span class="token comment">// 17:16:18</span>
<span class="token variable">$today</span> <span class="token operator">=</span> <span class="token function">date</span><span class="token punctuation">(</span><span class="token string double-quoted-string">"Y-m-d H:i:s"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>                   <span class="token comment">// 2001-03-10 17:16:18 (the MySQL DATETIME format)</span>

Timezone

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

<span class="token function">date_default_timezone_set</span><span class="token punctuation">(</span><span class="token string single-quoted-string">'Australia/Melbourne'</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token function">date_default_timezone_set</span><span class="token punctuation">(</span><span class="token string single-quoted-string">'America/Los_Angeles'</span><span class="token punctuation">)</span><span class="token punctuation">;</span>

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