If I say descend, I mean descend. I thought the old BOAC( the company, not the poster) attitude had gone forever. I do say "when ready" if I`m not too bothered when it happens and I`m not (usually) too disgruntled if the instruction is queried unless RT loading is high. The word "now" is useful, but I reserve that for occasions when stressing it is a good idea. "Immediately" is reserved for very unpleasant situations.
A colleague (since retired) was once heard to reply to the query "do you mean descend now?" with "No, I meant then"