Depending on traffic I'd allow 30-45 min from Disney. How long it will take I think depends a lot on how crowded it is and who is in your party. It is geared primarily towards children from about 3-10 but the nice thing about it is the adults who go along will enjoy doing a lot of the activities along with them. Price is very reasonable for this age group & the adults accompanying them. I don't think it holds as much appeal for teens & adult only parties & would see it as overpriced for them & they'd probably only need about 2 hours to do everything unless it is very crowded (which it often is right now on weekdays before 3 due to lots of summer camp groups being there). Also, you pay full price for 2 year olds and would be very limited in what a young 2 yr old can do so I think it's a little overpriced for them as well (under age 2 is free).
That said, I have a 4 yr old and she LOVES it! She could spend all day there & I have let her stay as long as 6 hours. Average family with kids in the age bracket it's geared towards I'd say 3-4 hours. It's indoors & air conditioned so great on hot & rainy days. They have 2 small playgrounds (one for 4 and under, one for 3 and up although nobody polices ages) as well as tons of art activities. I recommend seeing the show once (it's a 15 min show about how crayons are made, nothing to do with silly putty). While it's not on the level of a theme park show it's very informative & what Crayola is about & my 4 yr old doesn't find it to be boring at all while I see it as a good educational opportunity for her. You get 2 tokens every time you enter (even with an annual pass) and there are 2 activities that require 1 token so you can do each once. You can buy additional tokens for 50 cents each but I've never needed to.
The food they serve is very limited and not that great but the official policy is no outside food (not that they check bags). You can leave and re-enter so we just go to the mall food court, which has lots of choices & is a really short walk away (you can enter & exit from either the parking lot or directly in the mall).
I'd recommend it to anyone with young kids, especially if you get stuck with a really rainy day or need a break from the heat. Gatorland is about 20-25 min from the mall on the same road so you could always do a morning at Gatorland, afternoon/evening at Crayola (it closes at 8) to make the drive more justifiable.