I used to be an assistant to the School. I would time talks. I would frequently see small children barely able to go to school get up and have to read the Bible. Never mind that when I was their age, I was the only one in my class that was reading first-grade material fluently. Yet they would be reading words like Nebuchadnezzar, and would be expected to read it fluently. I have seen many of them reach 5:00 (the allotted time) before getting halfway through, and you could not follow them because they just couldn't pronounce the words fluently. Of course, they would get a W for fluency.
I also saw a few talks that were short (under 4 minutes). When this happened, the conductor would always suggest the addition of more material to round it out. This was normal for those #3 and 4 talks to run short. Very often, there simply wasn't any material that would be worth adding.