Make Blizzard IV instant. Here's why:

[Sensyon]

snip

I don't think you're examples are very good. If you hit Benediction or Hallowed Ground it goes off. It might be too late, but it registers. Using B4 3 seconds out, then having to interrupt, will require another ~3 seconds. So now its plan further ahead just in case. Interrupt twice and now you need more than 6 seconds, and so on. Also, no BLM was not always played this way. In 2.X, AFIII falls off you put it back up with a single cast. Enochian falls off and you're using you're 2.0 rotation for 30 seconds...