At least every 15 pages. Per the “Whammo Theory” told to me by producer Larry Gordon, a script should have something go “whammo” every 10 pages. It depends on the genre and type of story. And, of course, the ‘whammo’ is scalable, if it’s a small, character-focused drama, a kiss or a confession can be a ‘whammo’.
But to your point, Mark, when we look at a story in that light during the crafting process, targeting a ‘whammo’ every 10 pages or so is, as you suggest not “intimidating or unobtainable”. Indeed, it can make the process more manageable and less scary.