I made sure that the site settings had the correct timezone, as well as the server having the same timezone in the php.ini and htaccess files. The hosting company also confirmed this, which is ‘America/Jamaica’.
7 installed plugins were identified that had the function ‘ date_default_timezone_set()’ that the error made reference to. I disabled all of them and the error disappeared. I re-enabled one by one and the error re-appeared when simple-membership plugin was re-enabled.
In other words, whenever Simple Membership plugin is deactivated the error is gone and whenever it is re-activated it comes back.