You don’t have a lot of tools at hand. You can’t do much about the spell if the caster is maintaining it. Interfering with the caster directly would be very dangerous while in etherform. And you can’t do much about the inside of the box due to the silver.
But the outside of the box is far enough from the silver that you can affect it. So, without really having a plan, you age the pitch.
It starts hardening. Flame flows into it, and it starts burning, but the fire isn’t spreading. You don’t know what to do next, though.
As it turns out, you don’t have to think very hard about that, because there’s a sudden loud noise. It doesn’t really affect you, since you just perceive it as sound ether. But you notice the figure at the top of the tower falling off…
And vanishing suddenly before they hit the ground. Leaving a trace of what is clearly time ether. That worries you.
Meanwhile, the box is still moving. Probably because the wizard is somewhat protected from the noise itself by the box, and from the ether by the silver manacles. Their pace seems to have slowed a bit, though. You accelerate the fire on the outside so it burns out.
The bolt is no longer being maintained. You decide to investigate the tower, to see if the wizard inside has vanished like their cohort, or is simply unconscious.
You find something inside that you weren’t expecting at all.
Birds