Here's his website. He's a dynamite resource.
Eight seconds wouldn't be a problem, after all there are no areas which you need to dodge. After you get the light areas right, increase the grade a bit to get the dark areas of the background sorted out and adjust the time to keep the fur white with details.
Did you see Mr.Carnie's very interesting thread, above this sub-forum, as a sticky. . .
You've had lots of advice to make it even better so the only thing I will say is: Your split grade attempt is a quantum leap forward. Well done
This bears repeating: Split grade printing adds nothing but needless complexity versus a single exposure with an intermediate filter, unless separate burning and dodging manipulations are done during each of the soft and hard grade exposures.
Ok. So this is where I am now.
4secs with the 00 filter, 6 secs with the 5 filter, and then 4 secs added to the edges for vignette. I also had to dodge the cats left eye during the #5 filter to keep it from going 'dead'.
Grade 3, plus your burning-in then ?