Let me start by stating that this is my opinion based in my experiences. I welcome all others opinions, perspectives and criticisms.
Mid-August is a transitional time for crowd levels. The schools in Florida are starting back up at this time so mid-week crowds can be lighter than the weekends when locals and residents are trying to get in that last weekend before going back to school. So I would consider Mid-August as moderately busy but not crazy like spring break.
One thing you do not mention is how many would be in your party? This can make a big difference in how you get through not only these parks but any park. I have based my opinion on our group now which is usually between 2-5. When it is just me and my wife we can do a lot more than when it is the rest of my family (all teenagers now but when they were younger it was a completely different dynamic). Considering this, I think three days could get it done at a reasonable pace. Two full days in each park from opening to close and a third day to get to things that you may have missed or would like to do again. Now this is to do "EVERYTHING".
Why do I think this and how did I come up with 2-3 days?
One thing that has always thrown my time management out the door has been doing shows that are at a scheduled time. You would think that this would be helpful but unfortunately for me it never seems to fail that I have just gotten off an attraction and noticed that Fear Factor will be starting in 30 minutes but there isn't a ride close by without a wait time of less than 30-45 minutes. So now I either have to wait for another Fear Factor show later in the day or wait 30 minutes on this show. Now what do I do for 30 minutes, maybe go get a a pretzel. Some simple math, and I know this is painting a broad brush on wait times but just go with me here for a minute. Universal Studios has 12 rides. At just a moderate wait time of 30-45 minutes per ride that's a total 6-9 hours just waiting in line. Add about 5 minutes per ride there is another hour. Now add a few shows Horror Makeup Show, Fear Factor and Teminator at 1 hour each you are now at 10-13 hours and you haven't stopped for lunch or dinner or stopped along the way to just take in the sights and sounds, or get my pretzel. Now these numbers can easily be debated but I think you can see where I am coming from without going into a lot of detail. To do "EVERYTHING" it will easily take 2-3 days. Now does the average person do "EVERYHTING"? Probably not so a well planned out day could be done in 2 days but if you have never been there before and do not plan on returning anytime soon why put that stress upon yourself.