There have been homologated riders who were tardy at intermediate controls but I would not count on it myself.
If you average 22 kmh that gives a riding time of 55 hours, which allows for 16 hours sleep easily but can you get 2x 8 hours....? It would take a lot of planning to make a good estimate but off the top of my head.....unlikely.
I did around 75 hours in 2019. On the way out, I slept almost 3 hours at Fougeres, 2 hours in the midday sun in Loudeac, and 6.5 hours in Brest. I took a nap in the sun in Loudeac (not sure how long....maybe an hour or so) and then 6 hours in Tintineac for around 17 hours total. I wasn't killing myself on PBP in 2019 but it also fair to say, I can be a faster than average rando.
Your speed numbers suggest to me, given being very efficient at controls, you could start in an early 90H group and get to Carhaix and get a full 8 hours sleep Monday night. Wake up and ride to Brest and return to Tintiniac for maybe 4-6 hours sleep and if all goes well, a nap before smelling the barn.
A possible alternative is you truly can average 23 kph would be starting with the 84H riders Monday at 5 am and if you are financially able to use a travel agent to book rooms for you, to do PBP as 3.5 days and 3 nights. There are riders who ride very little at night.
In reality, I would suggest trying a 200K and 300K.....if you like it, step up to the 400K. That should give you some insight.