If a default timezone is not set in your php.ini, then you get the following warning:
"Warning: strtotime(): It is not safe to rely on the system's timezone settings. Please use the date.timezone setting, the TZ environment variable 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 'America/Denver' for 'CDT/-6.0/DST'"
To get rid of this warning, open you php.ini file and set a value for date.timezone