Proper multi-level security doesn't allow access to the clock in anything other than the top level. You could just have a monotonically counter that is periodically synced to reality every minute or two.

I must be misunderstanding what you are suggesting, since what it seems like you are suggesting would never work. High-resolution timing information is available to user applications via numerous APIs today. Hyrum's Law, and common sense, tell us we can't just lose this feature of operating systems and expect applications to work.

You can construct a high resolution timer from shared mutable memory and multiple threads. It's simple. One thread increments a counter, and the other thread reads it.