Having been Crew myself I don’t believe this saves (hardly) any time to be honest. The only thing which takes slightly longer, and I am talking seconds, is putting the hot entrees on to/into the trolley that’s it. You still are serving a tray, offer a pastry, drinks etc.

You need to be organised and plan ahead that’s all, maybe that’s what the minority of Crew are struggling with.
I mentioned before I have seen variations of service galore in recent times , including meal order taken on the ground in MAN on a club world meal order pad. All hand run “with a galley operator”, needless to say they never finished the service.
It’s a meal and a drink, all hands on deck, job done no problem, well it shouldn’t be a problem.

on a side note, at last and finally, the “managers” as they are called seen sense and reverting to a service which worked very well for decades rest of the day, either meals followed by drinks or drinks, meal and drinks, depending on route, rather than wanting to serve everything at the same time which was messy and took forever. That was another invention they hailed a success but finally they given in as this worked very well in Eurofleet and Mixed Fleet days but needed to change apparently, with Heathrow Cabin Crew starting. They call it a change and omit to mention that it is going full circle, says it all really.