<?php
$date = new DateTime("now", new DateTimeZone('America/New_York') );
echo $date->format('Y-m-d H:i:s');

<?php

$usersTimezone = 'America/New_York';
$date = new DateTime( 'Thu, 31 Mar 2011 02:05:59 GMT', new DateTimeZone($usersTimezone) );
echo $date->format('Y-m-d H:i:s');

<!-- wp:code -->
<pre class="wp-block-code"><code><?php

// Date for a specific date/time:
$date = new DateTime('Thu, 31 Mar 2011 02:05:59 GMT');

// Output date (as-is)
echo $date->format('l, F j Y g:i:s A');     

// Output line break (for testing)
echo "\n<br />\n";

// Example user timezone (to show it can be used dynamically)
$usersTimezone = 'America/New_York';

// Convert timezone
$tz = new DateTimeZone($usersTimezone);
$date->setTimeZone($tz);

// Output date after 
echo $date->format('l, F j Y g:i:s A');
</code></pre>
<!-- /wp:code -->

<?php

// Create a datetime (now, in this case 2017-Feb-11)
$today = new DateTime();

echo $today->format('Y-m-d') . "\n<br>";
echo "---\n<br>";

$oneWeekFromToday = $today->add(DateInterval::createFromDateString('7 days'));
$twoWeeksFromToday = $today->add(DateInterval::createFromDateString('14 days'));

echo $today->format('Y-m-d') . "\n<br>";
echo $oneWeekFromToday->format('Y-m-d') . "\n<br>";
echo $twoWeeksFromToday->format('Y-m-d') . "\n<br>";
echo "\n<br>";

2017-02-11 
--- 
2017-03-04 
2017-03-04 
2017-03-04

$today = new DateTimeImmutable();

echo $today->format('Y-m-d') . "\n<br>";
echo "---\n<br>";

$oneWeekFromToday = $today->add(DateInterval::createFromDateString('7 days'));
$twoWeeksFromToday = $today->add(DateInterval::createFromDateString('14 days'));

echo $today->format('Y-m-d') . "\n<br>";
echo $oneWeekFromToday->format('Y-m-d') . "\n<br>";
echo $twoWeeksFromToday->format('Y-m-d') . "\n<br>";

2017-02-11 
--- 
2017-02-11 
2017-02-18 
2017-02-25