It seems like I'm the only one the thread who has actually tried Nasus jungle so here we go...
I afk farmed Nasus about 25 times just because it's more fun than actually playing the game with you people.
A full clear gives you 84 stacks. With max movement speed items you can get 1000 stacks in 40 minutes. Most games will be on pace for 1000 stacks in 60 minutes.
Give yourself 10% starting CDR, then rush another 10% CDR item. 20% CDR in the jungle is all you'll need for the first 30 minutes.
Don't fully complete your jungle item. None of them are good enough for Nasus. Eventually you'll want to sell it for 700g.
Don't gank until you reach 999 stacks.
Also, start wolves, then blue, then gromp. Back. Then red, then birds, then prepare to fight to the death with the rocks. Still working on trying to avoid that.
In all seriousness though, nasus jungle is far superior to lane Nasus. The early stacks you get make you an early game powerhouse. 200 stacks by 13-15 minutes is easy