The best time to foliar feed is before the lights come on or the sun comes up, BUT the plants have to be dry when the light comes on or the sun comes up because if the plant still has any moisture on it’s leaves it will burn them like burning a bug under a magnifying glass. If you do not have enough time to foliar feed your plants before the light comes on or the sun comes up, then you should foliar feed after the light goes off or the sun goes down.