Plenty of US enroute/terminal controllers use climb or descent rates/FPM when trying to separate acft. But as mentioned before it is not a legal clearance here in the USA. I have seen a couple of controllers buy a separation error aka deal when using this procedure.
It is really easy to use a navaid or point in space to cross since most aircraft have better equipment then we use. Even a time to climb/descend clearance works well and as long as you learn the phraseology, just keep in mind the winds aloft.
For Isaidrightturns : you are probably right that he wasn't slamming us, I just read it after working busy sectors all day with weather and a new culture being implemented here...Regards CZHU