One other thing to keep in mind is that you could have multiple SLAs. I assume you want to limit this clock to the overall SLA, but you may also want one for the assignment level. And there could be a number of assignments, each with an SLA. So I guess the two pieces to your question are 1.) how to display a clock on the UI. Pahni's suggestion about the session timer is a good place the start. The second part is where are you getting the data to drive that timer, and that really depends on which SLA you want to track.