<?php
  $date = strtotime( '2018-03-07 20:48:21 America/Toronto' );
  echo date( 'Y-m-d', $date ), "\n";
?>
Output
2018-03-08
$d = 1394243280; // string is turned into a number

echo date('Y-m-d', 1394243280), "\n";

Number is converted to a date/time string using the default timezone: