If you wish to eat a full meal on the plane, then I am afraid you will not be able to. The Sleeper Service hot meal is still a regular size meal, and comes with a dessert too, but it is all served at the same time and very quickly after take off. By all means, you can be as leisurely about eating it as you wish, however, as you say, you understand the idea of the service style on these flights, so cabin lights will be out very quickly and any additional drinks will be brought by hand with only one bar service immediately after take off.

A full service is offered in Traveller and Plus as they do not have the pre-flight dining option, and in First, because it is First and you can choose to do as you wish in terms of catering and service is more discreet to allow others to sleep if they wish. However, trying to do that with 56 on a 777-300 out of JFK would just not work in terms of allowing those who wish to sleep to sleep, and those who want a full service to have that.
As you already appreciate, CW is a Business Class product, and these flights aim to maximise the sleep time available to people to enable them to do business at the other end. A 2.5 hour meal service on a 70 CW seat 747 would not allow this on a 6.5 hour JFK-LHR flight...