I'm in a part 141 program and in ground school. My instructor dismisses class very early almost every day, but in the logbook he keeps for us he writes a lot more time than we actually meet on any given topic. Is that okay?
A Ground School Syllabus needs to be checked and approved by the FAA. As part of that approval, they will decide if it meets minimum requirements, and is expected to take the required hours.
If the actual delivery of the material in ground school takes a bit less (or more) time than approved, that is OK, so long as the approved syllabus is closely followed.