Ira Glass is accustomed to working at the speed of public radio. Shepherding “Sleepwalk With Me,” the IFC feature he co-wrote and produced with “This American Life” regular Mike Birbiglia, was an entirely new experience.

“It’s shocking you spend three years on something that’s this short,” Glass quipped at an Aug. 28 screening and Q&A hosted by the Writers Guild Foundation and L.A. pubcaster KCRW at the Writers Guild Theater in BevHills.

Birbiglia was humble about his learning curve as a first-time feature helmer. “During the editing process we realized we didn’t know what we were doing when we were filming.”

The screening drew an eclectic mix of “This American Life” devotees, including Tom Hanks, Tim Robbins, Danny DeVito, “Mad Men’s” Rich Sommer and a surprise guest-moderator in Joss Whedon. Glass and Birbiglia reprised their recent on-air rivalry with Whedon by vowing “Sleepwalk” would top the B.O. of “The Avengers” no matter how long it takes.

Whedon took the high road and was effusive in praising “Sleepwalk”: “It’s a beautiful film. I’m a little pissed, I’m not going to lie.”