My fifteen minutes of fame class

Between increasingly frantic bouts of concluding, proofing, and footnoting, I'm grumbling about the loss of fifteen minutes from what used to be a ninety-minute class.  My lecturing has finally settled down into its new fifty-minute groove, but my ninety-minute class is...gasp...freshman comp, and that's a skills/activity-based course.  And I clearly have yet to gauge how to fit the scheduled assignments into the seventy-five minute period.  Part of the problem is that any in-class activity will require different amounts of time from course to course, depending on the number of students, their skills, the amount of caffeine in their systems, their enthusiasm for the course, their enthusiasm for each other, and so forth.  I've had exercises take one group thirty minutes and another group ten (!).   But this semester, we're not finishing things precisely because there's fifteen minutes missing.  V. frustrating.