Considering most movies are shot over the course of months, often with actors taking time to prepare and understand the role, it's a testament to just how much of a pro Christopher Plummer is that he was able to knock all his lines and performance in such a short window - and get a Golden Globe nomination for it, too.
In an interview with THR, Plummer explained that he'd originally planned on going on holidays before Scott called him - and that he'd actually met his character, J. Paul Getty, a party in the '70s. "I was living in London during the late ‘60s and ‘70s. And I had met Paul at a couple parties — that was all there was in those days, just party after party. But I didn’t get to know him or anything; I didn’t really know him at all. I just knew that the man was an extraordinarily rich chap with feelers all over the world and had made an absolute fortune."
Plummer also spoke about learning all his lines in such a short time, comparing it in part to theater. As for taking on a role again in such a short space, he says he's still up for it. "(It's) hard to digest when you’ve got all the other things to digest. I’m gonna see it at the premiere. And then I guess I’ll have to try to take a vacation again, won’t I? Then someone will call me and say, 'Somebody fell off a building, you better replace him!'"
You can read the full interview here.