timezone

Hi
In D7, When imported users login they get lots of error about the timezone

Warning: date_default_timezone_get() [function.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. We selected 'Australia/ACT' for 'EST/10.0/no DST' instead in format_date() (line 1862 of /Library/WebServer/Documents/MySite/includes/common.inc).

The site is set with a default country and timezone but I still get he errors

I added the timezone field the the CSV file with Asia/Singapore in the fields but still get the error

How do I set this up so the users get a default timezone if one isn't in the CSV file?

thanks