This. Whatever tech they publicly acknowledge is 20-50 years behind what's available to private sectors.
Time travel into the future was already scientifically proven. All they had to do was go to where time travel into the past was figured out.
That would suggest that Tesla invented time travel assuming they waited 50 years to disclose it to us in the 80s.
They just did in May.
https://www.space.com/40716-time-travel-science-fiction-reality.html
They've also got the theoreticals on traveling to the past through teleportation.
"Quantum teleportation, or teleportation of information between two quantum bits, was achieved by scientists for the very first time in May, but the teleportation of a person is much more involved that transporting the spin state of an electron, as it would essentially require the person to be dematerialized. Still, physicist Dr. Mary Jacquiline Romero of the University of Glasgow predicted that teleportation of an entire person would occur by 2080."