AFAIK thread entries don't have fields that you can configure directly. But a mod for staff is possible. Fields are for the ticket as a whole, the staff or the client. . Not the individual entry in the thread.
If it's simply time you could try my duration mod which bypasses an entry field by simply calculating the time between entries: http://www.forum.osticket.com/d/discussion//mod-time-duration-in-each-message That way staff can't cheat by saying they spent an hour working when the ticket has only been open 20m.
Please explain the second one further.