How to reset an application variable daily

I am writing a program recording service calls and treatment done. We have a number of users who open and close calls and I want to show at all times the total number of calls opened today and the total number closed today and the difference between them. I thought of doing it with an application variable. I have to reset these variables to 0 every day. Where would I do that? I thought in the Global.asax but in which event could that be done? The application is running all the time so I suppose Application_Start wouldn’t be appropriate. So where? Thank you.

Pass master page control values on content page on page_load

I have a dropdowlist on master page and I want to pass the selected value on content pages when a content page loads. My problem is that the value passes only when I change value on the dropdownlist. So when a page load I have to reselect from dropdownlist to capture the value of the dropdown. If I am browsing the content pages the selected value doesnt pass on page load.
My master page code .net: