Your assumption is correct that it really doesn't take that long to seat everything in or the rings and such but the bigger risk is leaving the metal shavings and contaminants and all the grit in there for too long.
I'm happy some engine manufacturers still tell people to do this the proper way.
I do hundreds of mowers every season and you can always tell when an engine still has its factory fill oil in there because it will have a gray metallic sheen to it.
This is not good.
This is the only time the oil in a small push mower will ever have that tint or metallic to it UNLESS it is run dangerously low on oil almost to the point of snapping a rod or locking up and scoring the cylinder wall.
I would say at least two Mo's mainly for the hot cold heat cycle but three would be fine too so somewhere in the 2 to 3 hours I would change the first oil but the 5 hours is just fine also.
Don't know what all you're thinking about using and don't want to get into it about oil which is not nearly as bad here as it is in the Facebook groups but I'm not a fan of full synthetic or anything like that because it's just a waste of money because it's a lawnmower engine and they are low performance little turds and hardly any of them ever get worn out.
Like you just posted, a 20-year-old engine that still runs great.
Even with the typical neglect they've received they still hardly ever wear out.
You have to amazingly abuse them like running them without enough oil in them or hitting stumps etc or a massively overrevving one to actually damage these things or wear them out.
I don't think synthetic oil is necessary because you're going to get unbelievable life out of them anyways with just standard oil.
I also don't think you need to buy the Honda brand oil. Lol
Now there is a debate going on and some people who work at shops etc will argue about special oil for air cooled engines or even start to talk about zinc.
If you want zinc either get some 15 w 40 rotella or check the actual spec sheets and find a rotella because they do have straight 30 weight also that has zinc around 900 to 1,000 parts per million or just go buy some Valvoline VR1 racing conventional oil and not the synthetic because it has like 1100 or 1200 parts per million the last time I checked.
THEN YOU'LL HAVE A FEW PEOPLE THAT WILL COMPLAIN THAT YOU HAVE TO PUT 10W30 IN A HONDA BECAUSE IT SAYS THAT ON THE SIDE.
Whatever pedantic people who think there's only one way to do everything. Lol
The fact is you can run about any oil you want to in these things and they are still 20 plus year motors.
There's absolutely zero reason you need to put a multigrade 10W30 oil and a Honda GCV or similar engine and a standard 30 weight will work just fine.
In fact, I believe the 30wt gives us better protection than most 10w30s in most situations.
Others will argue but nobody has any proof to back it up so it's all just opinions and preferences.
I know I've never had a small engine out of the 10,000 plus that I've worked on that ever had and all related failure that was anything other than a lack of oil!
I can also tell you I've seen thousands of them run on SAE 30 or hd30 and they're still going fine.
The only exception that I know of is for the old color commands with hydraulic lifters and if you used SAE 30 in those you can end up getting a clicking or tapping sound that wasn't very favorable so those get 10w30.
Hondas, Chinese built once, and everything else gets 30 and it's just fine.