Try Quartz.NET. It’s a decent .NET scheduler which supports CRON expressions, CRON triggers and various other means and methods to schedule tasks to be performed at certain times / intervals.
It even includes a basic Quartz.NET server (Windows Application) that might fit your needs.
Edit:
If you can’t run applications or windows services within your shared hosting then perhaps something like “Easy Background Tasks in ASP.NET” will do you? It simulates a Windows Service using HttpRuntime.Cache and removes the need for any external dependancies.