insert a php countdown to the chat of live support (livehelperchat)

I need to modify the live helper chat, a open source live support chat system ([login to view URL]) to insert in the chat system a countdown clock: the user starts the chat, the first operator takes the chat and set up the chat duration in minutes in the countdown, then, starts the countdown and both the user and the operator will see it on the chat window. when the time finishes, the countdown clock closes automatically the chat. if the operator transferts the chat to another operator the countdown clock continues it's work and nobody can stop it. (only the operator that set up the countdown will have permission to stop it, no other operators). The chat software is open source and you can download it to see if you are able to modify, so please make offers only if you are able to do the job.