Using System.Timers.Timer in asp.net

ASP.NET applications will get shut down when not in use. If someone hits your site, and then no more hits, it can get shut down. Your timer won't fire.

For this type of maintenance work you want to use a windows scheduled task or windows service.

Since .net 4.5.2, there is a class called HostingEnvironment, it can do what you're asking, here is how to use: https://blog.mariusschulz.com/2014/05/07/scheduling-background-jobs-from-an-asp-net-application-in-net-4-5-2

The HostingEnvironment.QueueBackgroundWorkItem method lets you schedule small background work items. ASP.NET tracks these items and prevents IIS from abruptly terminating the worker process until all background work items have completed.

Check this out... Jeff Atwood actually discussed something similar. I guess it worked, but according to Jeff the site outgrew this method so they went to a dedicated task.