Not very long, if customers follow directions and leave them alone for a day or two while they learn. Young stock may take longer than cows. The best time to train is prior to frost, when the drain hole can be plugged. Livestock then get water immediately upon pushing the lever. As your FFNP is installed at a very mild angle towards the back, there is always a small bit of water the animals cannot reach.  As they become motivated (thirsty), they will move the lever to get at the small amount of water at the back of the pump.  In turn, they will discover that every time they move the lever, they produce more water to drink.  Your most assertive animals will learn very quickly and then will train others.