I think you can use Response.Cache.SetExpires
method as descrived in How to: Cache Versions of a Page Using Parameters.
The code will be something like:
var tomorrow = DateTime.Today.AddDays(1);
Response.Cache.SetExpires(new DateTime(tomorrow.Year, tomorrow.Month, tomorrow.Day, 6, 20, 0, DateTimeKind.Local)
Response.Cache.SetCacheability(HttpCacheability.Public);
Response.Cache.SetValidUntilExpires(true);
Response.Cache.SetVaryByCustom("RawUrl")