Basically PHP doesn't know which timezone you're in. Thus it is telling you that your system time is unreliable without this modifier.
By the looks of the error message you most likely did something like the following :
Code:
date_default_timezone_set('3.0/no DST')
which is NOT a timezone.
Without the actually line of code I can't tell you. However I would suggest you do what has been advised in the error message and alter (or add) the line like the following :
Code:
date_default_timezone_set('Europe/Moscow');