I agree that United would need a manager in place soon to avoid a Moyes Summer - he wasn't officially in position until July 1st, we clearly hadn't planned ahead, other clubs knew it too and we got taken for a ride all Summer. A lot of our current issues can still be traced back to that summer.
However, what can United realistically do to avoid a late appointment? Your opinions will obviously differ, but for me the only candidates I believe are about the level of Klopp/Guardiola are treble winner Luis Enrique or coach of the year Thomas Tuchel. Tuchel. Even if they were both interested they are both contracted. I think ten Hag has the potential to reach that level, but again isn't available for another 2 months at least. If Pochettino is the one they want, same story.
If we want the better managers, we have to accept they're going to be contracted. I'd personally rather wait until January and get the man I believe is the very best for the job who'll seriously challenge Liverpool and City, than get someone lesser just to get them in quicker.
But it's a serious question, what would you do? Unlikely they'll be bought out a couple of months before the end of the season