I've come across this article, talking about a small rule change that happened in Born of the Gods. To sum it up - doing something to an illegal target isn't intuitive. The rule change is said to be also for older cards such as Frost Breath.
Now I have to wonder about Time to Feed - The interaction with an illegal target as mentioned in the FAQ also doesn't feel intuitive. Any reason the ruling for that card hasn't changed?

Originally posted by CR 701.10b:

If a creature instructed to fight is no longer on the battlefield or is no longer a creature, no
damage is dealt. If a creature is an illegal target for a resolving spell or ability that instructs it to
fight, no damage is dealt.

Because that rule exists, the interaction may seem a bit different. Also, the examples you cited - Frost Breath / Sudden Storm - try to affect their targets (they don't untap); if Time to Feed resolves, then there's a delayed triggered ability (DTA) created, even if one of the two targets is now illegal. That DTA isn't affecting the target creature in any fashion, it just triggers when (if) that creature dies this turn.

I hope I've correctly inferred the right questions to answer?

d:^D