Lined up to enter Williamsburg Cinemas in Brooklyn for a Thursday evening showing, some fans said they had deprived themselves of liquids for most of the day to avoid even a brief departure from the theater.

Standing toward the back of the line in the cold April drizzle, Kevin Myvett, 28, said he had spent much of the last week preparing for “Endgame” by exercising self-control and watching older Marvel films back-to-back without letting himself take a break.

“I was really trying to prepare myself mentally for this,” he said.

Fans and websites circulated tips on which moments were opportune for quick getaways. At an AMC theater in Inver Grove Heights, Minn., a suburb of St. Paul, Dylan Novacek, 23, darted from his seat during a scene that fans online said was not particularly consequential. He was back in about a minute. “I didn’t even know how he made it to the bathroom so fast,” his girlfriend, Kayla Erickson, said.