If you look towards the footer of every page, there is a line of text that states "All times are GMT". Since this is a site used by travelers the world over, there's really not a "good" local time for anyone. GMT is a standard base time for any organization that spans the globe.

This likely helps to keep the threads in the right order and so forth. I suppose that they could add in some javascript that reads the local time from your PC. That's pretty simple code. I've used it in the past.