Well the title said it all...
I tried this command but it didn't work:
Command: /set chattime <on|off>
Description: Enables time display for chat messages. Includes all Pms, Local, Group and System chats. Excludes server, new player or death messages. Useful for Screenshots.
Removing the new/departing messages is not possible though it is being worked on.. Or is in the ques to be worked on... In the meantime though having an expanded chatlog would be nice, as this has already been developed it would just be a matter of asking for it or possibly buying it from the guy that did. Both together would be amazing.