The term "plating-up" is kindofa misnomer. I prefer the term "uptake."
When the oil carries either the Zinc Alkyldithiophosphate (ZDDP) or Molybdenum Trialkyldithiocarbamate (MoTDC) in solution to the metal surfaces, they both behave as friction modifers (under light load) and when heavy loads are applied, they go into their Anti-Wear/EP modes; ZDDP at lower temps and lighter loads, and MoTDC at higher temps or higher loads. For moly, the molybdenum-sulfur-carbonate mixture forms a three-tiered set of layers (now containing molybdenum-sulfur-ferrous-carbonate) such that, when loads are applied (and surface temps go up due to pressure), the layers slide upon one another as a plastic layer of fluid, reducing friction and separating the metal surfaces.
For engines that have never run a moly additive before, the moly from an oil with this additive will show some "uptake" to the surfaces. That is, you will generally see some of the moly coming from the oil solution and adhering to the metal pores. This shows up as a subtraction of moly from the virgin oil solution.
So the answer is, the moly starts coating the metal as soon as the moly oil circulates, but the AW/EP action only occurs when the loads cause a pressure and temperature high enough to create this "plastic" interface.
From the gas law in chemistry, PV = nRT, the Temperature is a function of pressure,
(T = PV/nR), so when the surface pressure (load) between two adjacent surfaces cause the temperature to reach about 450 F or higher, then plastic flow on the surface occurs, inhibiting surface wear. (P is pressure, V is volume, R is a constant, and n is the amount of substance).
