The change should be pretty minimal in autos but if you are giving 20hrs of light and the plant is showing light stress symptoms like droopy leaves than cutting 2hrs from light (20/4->18/6) might help the plant to maintain better balance in everything.
So if there is problems too much light can make it worse but normal situation with autos it should not matter that much.
As long as the plant can handle the extra light, good things, but you do want some dark period, in general. There is such a thing as too much light, as long as you are below that threshold for the plant, it is a benefit.