Boring explanation for those above words below
The above tape standards had a "normal" max runtime of 120 minutes, and most of the tapes you see now are of this variety. It's not uncommon to see 90, 60, and even 45 or 30 minute tapes, some of which I seem to see more in "higher quality! (still metal particle)" variants, which may have just been an up sell. I don't know if it was actually useful to have smaller tape lengths to waste less tape during manufacturing or not. Of course, most recorders could do a lower tape speed LP mode, which doubles the runtime of any given tape in exchange for some quality loss.
However, 20 minutes is just hilariously short for this format. Yes, 20 minute tapes were fairly common for VHS-C (where anything above 30 used thinner tape AFAIK), but the whole point of video8 is that it had functional runtimes in camcorder size packages. Not only that but they show the reels in the packaging and you can see how little tape is actually in there. Normally a full spool would cover up the entire white area or just about. It's not some "ultra durable thick tape" or whatever it's just, a crumb of tape. An empty box of plastic.
Also, I do enjoy tape packaging a LOT. I will make a post about that some day.