Night Of The Living Dead, takes place the night at the start of the zombie apocalypse. Zombies are slow, simple minded, and stubborn.
Dawn of The Dead starts at the beginning of the outbreak, later than Night, but probably by a few days, weeks at most. Zombies are still slow and simple minded. They begin to exhibit the most rudimentary forms of learning/memory by returning to places they knew in life (initially, the mall, later the storage room). Tom Savini is killed.
Day of the Dead takes place some considerable time after the first two. Society has been overrun, which may have taken weeks, but also the military base has lost most of it's staff, is almost out of supplies, and even ran out of zombies! This is years after Dawn. Bub learns to listen to music, and shoot people.
Land of the Dead takes place a bit later than Day. A city has been built defended from the dead, people are speaking of retirement from their present jobs, and speak of loyalty earned with long service. This is years in the future. Zombies finally learn to think, use tools, hunt as a group, etc. Note how this took years, and years of growth and development, and was definitely not a thing that sprung up overnight - it has been incremental until this point. Despite previously being eaten, Tom Savini has managed to grow back, and becomes a zombie again.
Diary of the Dead takes us back in time to the same time as Night of the Living Dead. Zombies are simple again, and nothing interesting happens, except, halfway through is also the beginning of Survival of the Dead.
Survival of the Dead, therefore, happens slightly after Dawn of the Dead, and long, long before Land of the Dead, yet mere nights after the breakout, Zombies are seeing with ridiculously complex motor skills, one of them even being capable of riding a horse! This is flatly contradictory to the rate of education given to zombies throughout the other documentaries.
Given that we've seen early zombies capable of learning, which should not have been witnessed until late generation zombies, and we've seen Tom Savini both eaten by zombies, and then return as an uneaten zombie, does this mean zombies are capable of time travel?
