I'm afraid that I am struggling to work out what it is about the word "Descend" that people don't understand. It is an instruction, a command even. It doesn't mean "when you feel like it" or "when your on board computer feels like it" or when you've finished your coffee and the crossword. It means "DO IT". NOW would be nice. After all, if I say "turn left heading 290, closing from the left report established", pilots don't ask if they should do it now or at their discretion. Why should "Descend" be any different?
Rightly or wrongly I teach trainee controllers that when they instruct an aircraft to descend, it will, plus or minus the "wake-up-was-that-for-us" scenario and the inevitable short delay actually getting the thing to come down. But to all intents and purposes read "immediately".
There is nothing (that's ZERO) in the MATS Pt1 about "Descend when ready" or any equivalent. Descend IMMEDIATELY (my caps) is to be used only to resolve an urgent situation. The only bit that looks remotely useful is "Descend to reach (level) at/by (time/significant point).
For the curious or bored the MATS can be read at
http://www.caa.co.uk/docs/33/CAP493__Part1.pdf
then go to Section E (Attach) Page 3 and look for the Climbing & Descending bit.
Controllers do appreciate the economics of commercial aircraft operation and try to take that into account BUT there has to be a trade off with other requirements such as other traffic, sequencing, standing agreements with other units ad nauseum. With the best will in the world your ideal descent profile is going to be bent a bit. Don't add to it by causing controllers to mutter "Of course I mean bloody now!"