Endothermic atmosphere is prepared by reacting a mixture of hydrocarbon gas, typically methane or. propane and air, metered in a proportion such that there is just enough oxygen to form carbon monoxide. and hydrogen without excess carbon dioxide or water vapor.
But for your everyday run-of-the-mill deep conditioner, it should begin to work instantly, and reach maximum capacity at around the 20 or 30 minute mark. If your deep conditioner doesn't work after 30 minutes, it's time to ditch it for one that's more effective.
I left the Toner on the hair in 15 minutes, but you can leave it longer depending on how porous and brassy your hair is. just keep an eye on the hair and keep in mind that the longer you leave it, the more ashy it will turn out.