I think whenever you are hiding or not, Turn Bases buble should work normally - even if enemies don't know of your presence you should roll initiative and only act within their turns. Having characters in hiding act in real-time not only is too easy to exploit, but also just feels wrong. In my playthrough, I also had issues without summons not joining combat - I assume it had something to do with them being spotted.
I think allowing players or character far away act independently in real time is good, but they need to join combat zone if they get within striking range - stealthed or not stealthed.
