We went with our 1.5-year-old and 3.5-year old and spent half a day, though I'm sure we could have spent more time (it was just too darn hot that July day!). Our little ones really loved the Safari and of course the Triceratops Spin ride, which we rode four times. We spent time meeting Mickey and Minnie--that was lots of fun and we got great pictures. I think the kids would have enjoyed walking some of the trails and probably also Rafiki's Planet Watch (is that what it's called?) but the heat was just too much for them that day. We skipped all the shows because our toddler just wouldn't sit still for them, but I know there are lots of little kids who really love the shows and will sit through them. We're hoping to do those next time.
BTW, DH and I parent-swapped Dinosaur and Primeval Whirl; that worked out well.
From your counter it looks like you'll be going at a cooler time of year that we did so I think you could definitely make a full day of it if you want to.