Individuals can send messages in the color and font of their choice. As a rule, one can also choose whether or not to use a time stamp.
But a Chat log would have a date as well to mark when an IM session occured.
Why isn't there any dates? Because whoever forged these IM sessions didn't know where Foley was on what date.
Foley could if there were dates prove where he was, it is really that simple, and please don't try to tell me that computer don't mark everything done on them with dates we all know better. even pictures have date stamps as part of their file.