Just a thought,
When I say ''XXX123 climb FL210'' or '' XXX123 turn right heading 090'' or ''XXX123 contact xxx control on 136.555'' i dont include the word NOW yet the pilots do it instantly without question...
So why on earth if i say ''XXX123 descend to FL220'' does it cause so much confusion if I don't say NOW!!!!?????? It's a clear and simple instruction!!!! DESCEND means DESCEND, not descend when ready, or descend when you feel like it or descend when something shows on TCAS!!!
While we're on the subject, I also find it incredibly irritating to hear the classic ''XXX123 still on heading 165'' - Spaghetti Airlines are the worst offenders for this I think!!!