I don't know what PPO2 you are basing it on. Assuming a PPO2 of 1.6 and for a single daily exposure you have over 7 hrs before you reached 850 OTUs.Calculate it for yourself, tell me if my math is off.
It is highly unlikely a RB diver would plan a dive at 1.6 PPO2 and even if you were using an SCR with 32% at 130ft the gas in the loop would be something less than 1.6.
Now if you were talking about CNS clock you would have to limit your PPO2 to 1.3 to get a single dive exposure of 3 hrs