The time zone of the server running the script can be collected by using date_default_timezone_get() function.
If your error reporting is on then you will warning message saying
date_default_timezone_get(): 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.
So it is always better to set your own timezone by using date_default_timezone_set() function before using any date functions in your script.