Up until now, the chat logs have taken into consideration the time zone you have set in your member profile, and they are GMT time for people who aren't logged in.
However, they are now GMT time for everyone. This eliminates the confusion of a particular message towards the beginning/end of the day being listed under one date/page for one person and a different date/page for another person. This caused issues if people linked to a particular page of the chat log, or found a particular page of the chat log from a Google search, because the contents of the page (i.e. page 2 of August 1st) were different for everyone.