How do I model time passing differently for different characters?

I am the DM in this situation and a character has wandered into a small area which links to another plane. In this plane time passes differently, so 1 minute in that plane would be 1 hour in the real world.

Normally I would make sure the players just get equal screen time to ensure they all feel included, but this is complicated by the fact that the players in normal time are in combat, and the character inside the distorted time area is not.

If the player inside the time bubble were to immediately walk straight out, they would have been gone for a full minute, at which point combat would have likely finished.

How can I best play this at the table without making the player in the time bubble just sit around while everyone else fights?

I would also like to keep it vague, so the players outside of the time bubble don’t know if it is safe or dangerous inside it (IE: they worry for the character trapped inside), but the only way I can see this being accomplished is to deal with combat first, and anyone in the time bubble gets to sit out of the game until either combat is over, or everyone is in the bubble.

A good answer will draw from experience of similar situations, and ensure that everyone at the table feels like they are getting to do something. My players can be pretty slow in combat (and even slower out of it!) so sitting for a full combat might mean not doing anything for over an hour (actually worst in this situation because the nature of the combat in this area could well take the full session).

Addendum: The time distortion effect isn’t mandatory, and if I can’t figure out a way to deal with it properly I will just drop it for an easier to work effect, so frame challenges are not needed.