Also, to prevent getting into a bad habit, you should learn to l-cancel by only partially pressing L/R and not pressing it all the way down (or you could also just use Z to l-cancel instead). If you press and click it all the way down to l-cancel you won't be able to tech if you get hit and knocked down right afterwards.
The entirety of the hitlag of an aerial is included in the l-cancel window as long as the time after hitlag ends and when you land doesn't exceed the l-cancel window. So while the normal window is 7 frames I believe, if you connect with Ganon's d-air (10 frames of hitlag) 6 frames before you would land, all of the hitlag is included in the window, and you would actually have like a 16 frame l-cancel window in that case.
The hitlag will still use up the window though when included, and if the time after hitlag + hitlag is 7 frames or more, the window will cut off at the start of hitlag. This is what messes people up sometimes. Say someone were to press the l-cancel 2 frames before they would normally land, and would otherwise easily be within the window. If that same d-air were to hit 1 frame before landing, the included hitlag from it would use up the l-cancel window making the window end at the beginning of the hitlag, and makes what would have been 2 frames before landing then be outside the window and they would miss the l-cancel.
This is why you want to get in the habit of pressing the l-cancel only after the attack hitbox would come out, and not before.