J.O.
I am a firm believer in quality not quantity, you are upset about quantity, I have 7 kids in age from 16-16 months, and used to deal w/ the same thing, what I have learned is it isn't how much time you are spending with them but how much you give of yourself to them when you do spend time with them, even if all you have is 10 minutes every hour, during those 10 minutes are you giving them all of your attention and focus? If so don't worry you are ok, children need to learn that life and the world doesn't rely around them that they have to entertain themselves and that they have to learn to take care of themselves.
There constant fighting is VERY normal my 6 year old and 3 1/2 year old are at it non stop, and when it is really bad I send them to opposite side of the house to play alone, for 1 hour they can not talk to each other, look at each other, nothing. Know one other thing I do when they get a little older and have used this on all of mine at one point or another is I handcuff thier hands to each other it starts w/ one hour but if they can't figure out how to get along during that hour I extend it out even longer. I did this with my oldest and middle daughter once when we were out at our other sons soccer game,they just wouldn't stop bickering and fighting, they were so embaressed by people reaction, most though ti was great, I never ran into that problem again in public, my best friends family still brings it up and loves the idea and has even used it a time or two, I would wait until they are at least 5, The only reason I haven't done it yet with my two is that she is a lot younger then him and at an unfair advantage. I hope I helped a little good luck, you are so not alone, I feel your frustration!