Timer during Facebook Live.

What action should happen when the timer ends? Does the stack go into defense?
The timer ended with the spellbook open, or with a spell already selected, but the target hasn't been chosen yet. Will they allow you to choose a spell/target, or will it be canceled?
How will the timer start? Let's say I was attacked while I was away. I didn't have time to return – is that my fault? Or should there be a turn acceptance window before each round?

1. The stack definitely goes into defense.
2. If you didn't have time to cast the spell, it means you didn't have time.
3. The timer for the defending player and their actions should start when the button is pressed, and the battle should start immediately, so the attacker doesn't have to wait for the opponent to arrive. Perhaps a general pause button should also be added here, just in case something distracts the player in real life.