Timer stop

You say web page; is this an ASP application? If so, then what do you need to do in the server and what do you need to do in the client? It seems that the minimizing and maximizing would happen in the client; would the timer also be in the client? And for web pages, what if the browser has tabs? Are you refering to browser window or tabs in the browser when you say maximized or minimized?
 
You say "start counting when the window is maximized"; do you mean that you need the timer to restart when the window is maximized or do you need it to resume from the time that the window got minimized?
 
And what about when a window is restored,  not minimized or maximized? Most windows are neither maximized nor minimized.