easing up on his fastball when facing rookies just so they'd stay in the game.

on length of games and what caused them to lengthen.
One of the main culprits that was always noted was that the 'modern' ballplayer (post WWII) would go much deeper in the count than the old timers.

Many was the story of hitters who would go up swinging. Then along came Ted Williams. Williams would take 3, 4, maybe 5 oitches before he would start swinging.

Success breeds copying and Williams was certainly successful. So post WWII players started going deeper and deeper into the count. My recollection is that Wade Boggs, another Red Sox player was also famous for long at bats.

Based on those stories, I wouldn't be surprised that your stat on Johnson is probably true. I suspect Cy Young would be up there also.

Stories were that ball games would usually be done in 90 minutes with a few going as long as two hours.

Don't know that all that is true. Used to read Baseball Digest and Sporting News cover to cover and was always fascinated by the stories from the really old days.

Watching Cub games in the 60's, especially those Jenkins v. Gibson games, used to run 2:05. And that included commercial breaks between each half inning.

So, i have no doubt your estimate of 90 minutes is reasonable.

Figure 16 or 18 commercials and that adds 12 minutes, at least. Now, we only need to find another 20 minutes added over the course of around 50 years.

Pretty believable.

and the backing out of the box after every pitch to adjust gloves, scratch crotches and spit. Lots of little time wasters that have crept into the game that add very little.