Again, using the word immediately in descent clearance implicates some unnecessary urgency ?
In my mind 'descend' is sufficient, 'descend now' has become a necessary evil to reduce subsequent RT but should mean the same thing in terms of urgency ie do it when you can without unnecessary delay,
'descend immediately' means do it right now, there is a separation issue imminent and it is
urgent.
My pet peeve as a controller was a pilot stating 'ready for descent or request lower' (or variations there of) and me issuing a descent clearance and then getting the reply 'confirm that's when ready?'
I always tried to use when ready descent clearances where possible, but often had to issue 'descend (now)' clearances to keep thing moving effectively, there was of course a few examples where the level change was accepted early and effectively straight away, but descent at 100ft per minute etc catching their profile, which of course did nothing for saving RT...