Unix timestamps in PHP

Get the current Unix timestamp

$seconds = time();                              // 1700000000
$millis = (int) round(microtime(true) * 1000);  // 1700000000000

Convert a timestamp to a date

$dt = new DateTimeImmutable('@1700000000');
echo $dt->format('Y-m-d H:i:s');  // 2023-11-14 22:13:20 (UTC)

echo $dt->setTimezone(new DateTimeZone('Asia/Tokyo'))
        ->format('Y-m-d H:i:s');  // 2023-11-15 07:13:20

The @ constructor always yields UTC regardless of date.timezone; convert zones explicitly with setTimezone().

Convert a date to a timestamp

$seconds = $dt->getTimestamp();
$seconds = strtotime('2023-11-14 22:13:20 UTC');

Parse an ISO 8601 string

$dt = new DateTimeImmutable('2023-11-14T22:13:20Z');

A string with no zone is read in date.timezone. Prefer DateTimeImmutable over DateTime; mutation bugs in date code are hard to track down.