Easier way to configure both PHP and Database timezone under "System -> Settings" page.

Whenever enable or disable this extension, you will need to rebuild the cache.
1. Go to "Extensions -> Modifications", click the refresh button at the top right corner.
2. Go to "Dashboard", click the setting button at the top right corner, and refresh the theme cache.

* If this extension is not working in "Extensions -> Marketplace", please download it manually at the link below and upload it via "Extensions -> Installer". Don't forget to refresh the cache as in step 1 & 2 above after install.
https://www.opencart.com/index.php?route=marketplace/extension/info&extension_id=31349