I think it was early. Early enough for Master's founders to take some of the know-how with them in 1930.
Their first appearance in Akro ads of which I am aware was in 1931.
They are not in the 1929 ad I know about.
I can't remember seeing a 1930 ad, well, not a full Akro ad which listed the company line. (A 1930 advertisement from a distributor does mention Akro Tri-Color Agates ... the marbles known to some as Specials ... and I don't see Sparklers there but that doesn't mean anything.)
I still see Sparklers in an ad which I think which was printed in 1934 or later.
(I'm consulting American Machine-Made Marbles and this thread, http://marbleconnection.com/topic/10676-akro-timeline/, to refresh my memory.)