I've mained a scholar since launch and I just realized maybe I've been misinformed about when to cast virus.

I had always thought that the cast of virus needs to go off BEFORE the boss's cast begins for it to take effect. For example, for Gigaflare, Revelation, Critical Rip, Nerve Cloud, etc. I've always been predicting when those attacks will be coming up.

However, someone told me today that you can cast it during the boss's cast, as long as the virus effect takes effect before the cast finishes.

Maybe I've been gimping myself out/stressing about predicting big attack timing. Can someone please enlighten me? Thanks!