It is very easy to spend 20-60 minutes at each of the what is it....13 controls.
Most brevets I don't really care about time but sometimes, it is important to practice being efficient getting thru controls. I set a hard limit of 5 minutes on local brevets and am happy if it is 3 minutes. OP could practice such extreme efficiency in order to sleep. The drawback is constantly joining a new group on PBP.
OP mentioned 400K just being one sleepless night. I would think a little different. Most 400k in USA anyway begin at 4 am. With 20-23 kmh, you should try to learn to ride as efficiently as possible to finish around midnight on a not too hilly route. why? To get the kind sleep you need, you must be miserly with time at controls. In southern New Jersey, that is pretty easy but in Pennsylvania, it is pretty darned hard. PBP averages 1% or 50 feet of climbing per mile. Not really hilly but not flat. Often, randonneurs will do about 400k on the first day and sleep 3-6 hours. On my first 600K back in the day, I slept thru the alarm and the sun woke me up. I did not even pack my stuff. I jumped on the bike and put it on the big ring. I was late to the next control, but they let me slide as long as I finished under 40 hours. It took two years in a row doing a SR series for them to let us into PBP. Probably not a bad idea and would strongly suggest OP not have PBP be their first attempt. Maybe try a 1000K this year?? Sorry for the ramble.