I don't know what he meant, but void line solidifying is used by everyone I think.
I keep this rule in mind, never seen good example with or without it, yet I have more then a few that were very clear and accurate at the time, and all of them the void line became present on the day the void ended, not on the day day branch clashed it.
So I'm open that it may work if the day hits it on the day of asking, but not sure I have example with that.