they were chained in darkness for 70 generations. – a generation = 70 years, 80(if by strength Ps. 90:10) (70 generations x 70 years) = 4900 year imprisonment. Original punishment for Apkallu/Annuaki was to watch their children (greek mythology's Titans [their childeren = olympians, grandkids of apkallu/annunaki]) kill one another and eat one another for 500 years, then be bound in chains under the earth for 70 generations.
so… assuming apkallu/annunaki decend at Mt. Hermon in 3500ish BC (time of Jared, sixth from Adam) 500 years to watch them kill and eat one another, then into prision for 4900 years at 3000BC. Puts their release date around 1900ish AD. Generally around the same window of time of humanity going from illuminating dark spaces with an open flame =electricity; traversing great distance on the back of an animal or a boat => automobile/airplane/rockets.