I wouldn't be surprised if it needs a re-login, but I can tell you from experience that both of those methods definitely work. Personally, I actually use the "infinite delay" version.
I don't agree with there being "a simple toggle" - or rather, I don't agree that should be the FIRST thing to change about it. The GTK3 behavior is just Stupid And Wrong, and nobody wants it (except apparently someone at GNOME) at all, ever. I'd rather have the default behavior fixed so it just works the way it should.
AFTER that, the minority can already change it fairly easily if they want, and they even have the option to do so for all themes rather than just the current one. (Which is how it needs to be anyway since nobody sane is going to want behavioral side-effects from cosmetic theme changes). For MATE to offer a toggle for it though, first you have to fix all the themes to not randomly be inconsistent to begin with, or you're just making it even more of a mess than it already is.