Javascript Based Evergreen Timer with Persistent Cookies

Hello I am looking for a javascript based Evergreen timer - unique to each user. If a user goes on the landing page with the timer script installed and the timer is expiring in 10 days, 30 minutes and 40 seconds. The timer for that user should start at that time, when he visits the page and should expire in 10 days, 30 minutes and 40 seconds for that user. But if another user goes to the landing page after 4 days, his timer should start from this time and should expire in 10 days, 30 minutes and 40 seconds for that user. We have achieved this point. The problem we are facing is ---when we restart the computer the timer is getting refreshed for the User, when he is re-visiting the landing page. Let me know if you can do something like this. Thanks !!