It's happening because the value of 'time' has to be adjusted to match the times in Timestmp. In your case, it needs to be adjusted +13.5 hours. You can fix this by changing the Setup => Date Options => date_offset option to 13.5. I didn't do it on your installation since I'm not sure if you have anything else that's using dates (this will affect dates returned from GT::Date - you can make it only affect building by editing nph-build.cgi, and searching for where it uses date_offset).

Adrian