Unix Timestamp in PHP

time()                              // seconds: 1700000000
microtime(true)                     // float seconds with microseconds
round(microtime(true) * 1000)       // milliseconds

// Store in variable
$now = time();

$epoch = 1700000000;

date('Y-m-d H:i:s', $epoch)        // "2023-11-14 22:13:20" (local time)
date('Y-m-d H:i:s T', $epoch)      // with timezone abbreviation
gmdate('Y-m-d H:i:s', $epoch)      // "2023-11-14 22:13:20" (always UTC)
date('c', $epoch)                   // ISO 8601: "2023-11-14T22:13:20+00:00"
date('r', $epoch)                   // RFC 2822

strtotime('2023-11-14 22:13:20')    // 1700000000 (local time)
strtotime('2023-11-14T22:13:20Z')   // UTC string

// Using DateTime (recommended — timezone-aware)
$dt = new DateTime('2023-11-14T22:13:20', new DateTimeZone('UTC'));
$epoch = $dt->getTimestamp();        // 1700000000

// From local time
$dt = new DateTime('2023-11-15 03:43:20', new DateTimeZone('Asia/Kolkata'));
echo $dt->getTimestamp();            // 1700000000

$epoch = 1700000000;
$dt = new DateTime("@$epoch");       // @ prefix = epoch

// Display in a specific timezone
$dt->setTimezone(new DateTimeZone('Asia/Kolkata'));
echo $dt->format('Y-m-d H:i:s T');  // 2023-11-15 03:43:20 IST

$dt->setTimezone(new DateTimeZone('America/New_York'));
echo $dt->format('Y-m-d H:i:s T');  // 2023-11-14 17:13:20 EST

use Carbon\Carbon;

// Current timestamp
Carbon::now()->timestamp             // seconds
Carbon::now()->getTimestampMs()      // milliseconds

// From epoch
$dt = Carbon::createFromTimestamp(1700000000);
$dt->toIso8601String()               // "2023-11-14T22:13:20+00:00"
$dt->diffForHumans()                 // "2 years ago"

// To epoch
Carbon::parse('2023-11-14 22:13:20 UTC')->timestamp