No reference about a latest point, but the pilot should know the controler's intentions at latest before the threshold (which is already very late).
As said above, that's around 50'.
How many seconds before touch-down from 50' ? How much time does a jet engine need to rev from almost idle to TOGA ?
50' seems a bit late for a jet. On the other hand, I've used "Report VERY short final" with little mono-engine planes.
As ever, a good explaination before the fan is hit can help the pilot make a decision. I reckon "...Errr..." is not precise enough.