User blog comment:Thailog/Season 3 Preview Breakdown/@comment-29555595-20180722092036

According to this source on SyFy: http://www.syfy.com/syfywire/watch-sdcc-why-young-justice-was-and-still-is-ahead-of-the-curve-of-binge-worthy-cartoons

They said the first set of 13 episodes would release after Titans releases, then the second set of 13 episodes would release after Doom Patrol and Swamp Thing aired their 10 episodes

So I think they'll release the first half this year, and the second half in 2019