MySQL NOW() function - whose clock is used? For the mysql NOW() function, whose system time is used for time calculations? The host of the database or the client executing the statement?
That should be the time of the host (DB Server).
To be sure, login to MySQL from your client and run
SELECT NOW();

and then run the date() command in PHP and compare.
The NOW() and PHP date() would only be the same if you are running MySQL and Apache/NGINX on the same server.
CAPTAIN's LOG : SUPPLEMENTAL
You may also compare the difference between NOW() and SYSDATE() if you care about the datetime being deterministic.
The example in the documentation for [SYSDATE()] show how
mysql&gt; SELECT NOW(), SLEEP(2), NOW();
+---------------------+----------+---------------------+
| NOW()               | SLEEP(2) | NOW()               |
+---------------------+----------+---------------------+
| 2006-04-12 13:47:36 |        0 | 2006-04-12 13:47:36 |
+---------------------+----------+---------------------+

mysql&gt; SELECT SYSDATE(), SLEEP(2), SYSDATE();
+---------------------+----------+---------------------+
| SYSDATE()           | SLEEP(2) | SYSDATE()           |
+---------------------+----------+---------------------+
| 2006-04-12 13:47:44 |        0 | 2006-04-12 13:47:46 |
+---------------------+----------+---------------------+

Sorry, if this is WTMI, but just know that NOW() comes from the DB Server, not the WebServer.
Back in March of 2014, I talked about monkeying around with the server time and its effect on binary logs : Risk of changing clocktime on MySQL server host