These are show length times (not including waiting and seating and exit times)
Nemo - 40min
Flights - 20min
FotLK - 20min
TTBaB - 9min
Show total is 1:29, average seating/exit per show is about 5min total, so just under 2 hours for all shows.
These are ride lengths INCLUDING loading and unloading
Safari - 32min
Dinosaur - 8min
Kali - 10min
E:E - 6min
Train - 15min
Primeval - 5min
TTS - 4min
Ride total is 1:20.
Pangani and Maharajah are both 10 minute walks without actually stopping to look at animals. So, lowest estimate with at least stopping to see something would be 30min for those two.
Rafiki's/Conservation Station is about a 10 minute walk. Touring the building without doing any of the activities is estimated at 10 minutes (never done that). 20min total there.
Then we have the lines. Let's assume the park is at 1 out of 10 crowd level (as it is today, 10/16). We are looking at E:E and Kali at ~20min, Safari at ~30min, Dino and Primeval at ~10min, TTS at TTBaB at ~5min. Total for lines 1:40.
So, I suppose the 6 hour/half day would be possible. On the most empty of days, without actually stopping to look at much, without eating, without meeting a character, assuming the shows fall perfectly so you don't have to wait for them, without watching the parade, without watching any of the live entertainment throughout the park, and without completing any activities at Rafiki's, and with teleportation between attractions, it takes 5:50 to complete the park.
I'll stick with my earlier comment - I recommend a day and a half.