PHP Warning: date(): It is not safe to rely on the system's timezone settings. You are *required* to use the date.timezone setting or the date_default_timezone_set() function. In case you used any of those methods and you are still getting this warning, you most likely misspelled the timezone identifier. We selected the timezone 'UTC' for now, but please set date.timezone to select your timezone.
This simply means that the timezone is not set in your php.ini file. First find out where your php.ini file is. For example in /etc/php.ini. Open it and add the below line and replace with your timezone
date.timezone = Asia/Singapore
Remember to restart apache2