Marty goes back into videographer mode asking Doc questions about how the machine works, and what powers it. It’s in this moment that he learns it’s powered by plutonium – and not just any plutonium, but aDoc received after ripping off a group of Libyan nationalists.
According to Doc, the time machine runs on electricity but needs a nuclear reaction to generate the 1.21 gigawatts necessary to effectuate the time jump. That’s right, 1.21 gigawatts.
This is the moment where the film takes its first jump cut. We lose that flowing sense of real-time energy (it was fun while it lasted). But, of course, the movie itself really gets going from this point on. Doc fills the DeLorean with plutonium, packs his luggage, and prepares to bid Marty farewell when Einstein spots something in the distance.
Chaos ensues, resulting in Doc getting shot, and Marty forced to flee for his life in the DeLorean. I might add, by the way, that the car really struggles to hit 88mph and outrun the bad guys who are driving a rather large (and old) Volkswagen, but I digress.
While we cannot quite make out the “current” time on the Time Circuit LED panel inside the time machine, if we continue to go by the film running time (and assume we didn’t lose much time in the jump-cut), Marty – Casio on wrist – likely makes the leap to November 5, 1955, at 1:27 AM Hill Valley CA time, (1985) – where his adventure really begins.