Currently, timestamps in log files are stored in whatever the local formatting of the system is (for instance, I use a "." as my time separator, so a timestamp in the log file might look like "02.22.00"), with no time zone information. They should probably, for ease of keeping track of chronology (once there's a "better" log format, as has been discussed elsewhere) and for consistency, be stored in some canonical format, with some specified time separator and with time zone information (the aforementioned "02.22.00", in such a format in my local time zone, would be "02:22:00 -0700"). They can always be reformatted into any format the user wants, for display in message windows and log windows, but it's important that they be in a canonical format; otherwise, it is quite possible for somebody travelling with a laptop to send messages and subsequently have the history reflect that they were sent in an order other than that in which he sent them.
