Hi John. I don't want to get into the HIT (High Intensity Training) vs Volume thing, but some background is in order. Dr. Darden came up with Arthur Jones when he came out with his nautilus line. Their premise was, after a general warmup, you did a full body routine in a circuit, going straight from one exercise to the next , resting long enough to catch your breath, taking each exercise to failure for the rep range you are working in, and one set was all that was performed per exercise. You can see, that done that way, 30 mins would probably be close to the norm.
Now, is it effective? A lot of people think so, especially with beginner's. However, even Arthur Jones came out later and stated that for highly trained people, multiple sets might be better.
Splits, well even some hard core HIT advocates (MentzER and that huge Brit that won Mr. Olympia-forget his name) advocate splits. Personally, I don't care for splits much as I generally don't train bodyparts, but he, If you like them, upper / lower, or even a 3 way seem to work for others, and they seem to like them. My advice, start out with a full body 2-3X week, then as you advance, consider a split. Same thing with single vs ultiple sets.