Someone mentioned earlier (might have been in another thread) that it's the local time of each user's country. This seems though a little unfair if seats are not saved for those who live in the west :/
I didn't even try to book last week, so I don't know how all this works. Do you book through the regular booking engine? Is there any chance to book return from a different city, e.g. LON-BKK/KUL-LON?