"That experience is amazing, just to be observing," Temple said Canada's Cornwall & Area Pop Event.
"I'm a spoke in a wheel in that movie, which is fine, but to watch [Leonardo] DiCaprio, and Brad Pitt, and Al Pacino, and Jack Nicholson, and Kurt Russell, and Margot Robbie, Luke Perry before he had passed, God rest his soul... and then to have Quentin Tarantino overseeing it all, this guy is a mad man. He becomes his movie."
If Nicholson appears in Hollywood, word didn't come out of Cannes, where the film was received by a lengthy standing ovation in May. Speaking to Indiewire after its premiere, Tarantino said he might recut the two-hour, 39-minute Cannes version and "make it longer" ahead of its July 26 wide release.
"I wouldn't take anything else out," Tarantino said. "I'm going to explore possibly putting something back in. If anything, I wanted to go to Cannes too short. If I'm going to err, I'm going to err on too tight."
Nicholson was set to end a nine-year hiatus and star alongside Kristen Wiig in an English-language remake of Toni Erdmann, but the 82-year-old actor dropped out of the project last summer.
The Chinatown and One Flew Over the Cuckoo's Nest star's last appearance was in James L. Brooks-directed romantic dramedy How Do You Know, where he appeared alongside Reese Witherspoon, Paul Rudd and Owen Wilson in 2010.
But Tarantino, who explores 1969 Los Angeles in his ninth film, may have coaxed Nicholson out of retirement.
"He's so excitable, and he's so energetic, and he's exactly the way you think he is, and he's so passionate about the work," Temple said of Tarantino.
"And it's such an exciting day, and it's huge. I mean, it's Hitchcockian, it's the old school and the big camera rigs and big film canisters, and jib arms, and lights, and it's a great experience and the story. Quentin runs it all. This is his movie, and he is in charge, not DiCaprio, not Brad Pitt, and they fall in and they do great. It's gonna be such a good movie, and it was such a good experience to be part of it."
Sony Pictures opens Once Upon a Time in Hollywood July 26.