Yeah, try it out in training. I recorded 3 subtly different timings of 4B BE and had the dummy replay them randomly to make sure it can be evaded on reaction. Maximising your damage is the hard part since you wake up backturned.
Not sure if this has already been discovered, but I hate Cervy so thought I'd post it here anyway. Sorry for the awful quality...
You can avoid Cervy's 4B BE if you get up at just the right time. It's a little tricky, but you have to hit G as soon as you see the yellow flash. I've yet to try it out offline, so I'm not sure how practical it is just yet.
If you mess up the timing, you should still get up and block the attack anyway, so it's probably worth trying when you expect a 4B BE.