Discharge time limit
The maximum time concrete may remain in the truck between batching and complete discharge, after which it has stiffened and changed enough to be a different material.
What does discharge time limit mean?
Limits are typically expressed in elapsed time or drum revolutions from batching, and they tighten in hot weather when hydration runs faster. Exceeding the limit means the concrete has lost slump and started setting, and the standard fix of adding water is exactly what the specification restricts. Retarding admixtures extend the workable window on long hauls and large pours.
In practice
A truck that sat in traffic and then waited an hour on site is the load most likely to produce a cold joint or a rejected placement.