Confirmed : you can still walk around in Continuous Time Mode while your friends are in Combat Turn-Based Mode.
Now I'm curious to see if Larian managed to fix the ambushing difficulties, and all the things that could go wrong if some of your characters are not all drawn in Combat Mode at the start of Combat. The most basic solution was to apply Turn Based Mode to every creature around ... Well, who knows, perhaps Larian did this with combat start, and the 3rd demo-er has his character far enough ... but I'm not super confident.
