DC's Legends of Tomorrow : At this point, Stein's health must be in serious danger…

Given that its established that he needs to combine with Jax every so often to survive. Its been quite a while since that happened.

I think it's fine as long as they remain in contact and stay close. cause they always seem connected mentally

That we've physically seen. While it's week to week for us, most episodes don't take place back to back.

They might also periodically combine just for that purpose. But yeah, the show really stretches credibility on how forcibly they separate the two of them, despite Firestorm being the biggest gun in the Legend's arsenal.