I'm on over 10.5 rounds.
Usyk is a smaller heavyweight. He never was a huge puncher at cruiserweight and his power hasn't translated to knockouts of bigger heavyweights. At age 35 I don't think it will start translating now.
Joshua doesn't have one punch go-away power. His KOs have largely been the result of pummeling opponents with many shots or opponents walking right into his biggest punches. A defensive minded fighter like Usyk isn't likely to fall victim to either of those things.
I bet a line that isn't available anymore, but even at the currently widely available odds of -135ish the over is worth a unit.
Just my opinion...
What's the odds?