5 minutes or an hour will still cause the oil to begin to breakdown and not protect as well against wear. What temps does the 3600 rpm lawnmower hit? Without that info, all day with a lawnmower or 10 minutes in a mm is irrelevant, because you can't discuss if the oil is past it's ability to retain it's function.

Cb already told you what the mm will hit, and it's past the operating temp range of those cheap conventional oils. Does a lawnmower pass those temps? Or are you just assuming they do?

Have one briggs with over 800 hours and is in its 11th year, another Longtail we sold three years ago with over 1600 at that time, and is still going, a low hour Kawa that's 8 or 9, and a 10 year old Kohler at 650. Not one has ever run conventional oil cept for the Honda Longtail for the first two seasons. And yet, there are people here (one gave a specific example) with firsthand knowledge of the wear associated with the cheap stuff vs using the high zinc stuff. Also, many of these guys run their engines at 4600 for extended periods of time, but the heat generated at 4600 even for a short period can pass those temps at which the manufacturer and actual chemistry proves conventional oil starts to break down and lose some of its wear prevention properties.

Run whatever oil you want. You don't need me or anyone else to tell you what oil to use. But there is actual experience and evidence to prove the higher zinc oil can reduce wear. Will an engine run 2k hours using the regular stuff? Probably. Will the cam lobes be worn more than if you had used an oil recommended for this engine design? Very likely.