No Mike 5 nano-seconds ain't long enough! You need to be sure no one else is half way through something. Wait about 5 secs after you tune the new freq, then speak. Obviously you don't need to wait 5 secs after every other tx before you speak. About 5 nano-seconds sounds about right for some freqs. The long pause is inly on initial transfer to a new freq.
Is "maintain present heading" not properly acknowledged by "Wilco" then. Says it all if you ask me. Inderstood your tx and will comply. What else do you need? I agree "Wilco" will not do to acknowledge a specific instruction like "ABC turn right heading 360". Mind you even "maintain present heading" would be an improvement!