Hi BOAC...
The Mgr concerned wrote an article to address the "rumours"
As far as I recall, it was an "advisory", not a Warning / Caution. No actions were required, and all the advisory tells you (it was Lowish Qty) is that the Qty is likely to rise when power is reduced. Only when the Qty gets seriously low and/or (?) has Pressure/Temp associated implications are any actions required.
As far as I recall, he elected to reduce power, or even idle the engine. So I am not sure if it is relevant to this thread. There was no requirement to do anything other than monitor the engine, in fact not even that
and so the "idle" was purely at the crews' whim. It turned out there was a filter partially blocked that just restricted the Qty returning to the sump where the level measurement.
Therefore, IMHO the engine was not failed, faulty, unserviceable, and was able to produce full power if required, and there was no strict reason to believe that there was even a time limitation apparent - so he was technically correct, and could even be stated to have been "over cautious".
Please do not read into any of the above that I would have acted similarly. I do not know the full facts, was not in the situation, and as far as I know, there was no report published, other than his article, and doubt it got any further than an ASR.