problem after switch to litespeed in directadmin

[TakCloud]

hi
im install litespeed and build php
after switch from apache to litespeed my website this error
:
Warning: date() [function.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 'America/New_York' for 'EST/-5.0/no DST' instead in /home/mani/domains/manichat.ir/public_html/class/Index.class.php on line 64

how fix this problem?