There's no set schedule and not everyone thinks defoliation is good! I defoliate my autos when 1) I can't simply tuck under, 2) when I need to get air flow going through and 3) when some leaves are dying off anyway. You always want to go at it slowly so as not to stress out your plant. I'll take a handful of leaves off and wait a day or two to see what happens... if the plant doesn't take notice and I feel the need to do more, I do so... Generally, the leaves I will trim off are those that are covering other bud sites and not allowing light to get down to them. I PREFER to do LST early on in the game but sometimes, you just have to do what you have to do.... I defoliated the MOST on my Tangerine Dream grow... those two plants made a bloody jungle out of my tent and I was defoliating up to about a week or two before harvest. I didn't defoliate at all on my Big Bud.... you just need to judge your own grow!
Good luck!