WSJ had an interesting article about how much action time is observed for a typical baseball game: about 18-minutes in a typical 3-hr game, or about 10%.

Time bt pitches: 1:14:49
Time bt batters: 33:39
Time bt innings: 42:41

"....What's the bottom line? When we compare total action to total down time—even including debatable action such as pitches, trots and pickoff throws—total action time is 17:58. The average game time was 2 hours and 58 seconds, so the action portion of a typical game is 10%. That leaves 90% of the game as down time...."

The Action in a Baseball Game Is About 18 Minutes -