Most fights are scripted, so good tanks know when tankbusters occur down to their timestamps. It's not uncommon for a tank who is optimizing for difficult content to pop a cooldown 18 seconds in advance, knowing full well that the last two seconds will catch a tankbuster and allow the cooldown to be back up early enough to catch the next one. Also, historically, abilities like IB used to require you to anticipate cooldowns even at baseline levels of play.

I think that if you're trying to do something optional but fun, there definitely should be a timing challenge attached.