He began taking classes at the Groundlings in Los Angeles, an improvisational and sketch comedy troupe and school, while tutoring children to make ends meet. Forte's first successful foray into comedy was 101 Things to Definitely Not Do If You Want to Get a Chick, a comic book he produced that details incompetent men. The comics landed him his first professional job writing for The Jenny McCarthy Show, a short-lived variety show starring Jenny McCarthy. Shortly thereafter, he was asked to submit a packet to the Late Show with David Letterman and was told Letterman responded favorably to animation. After only nine months at Letterman, he was "let go" from the job. He recalled his stint on the program as unpleasant, noting that he did not have enough experience in writing. "What an honor to work at that show but I don't think I was fully mentally prepared. [...] I always wonder what it would be like if I'd had a couple more years of experience before going there."  Forte returned to Los Angeles and began performing with the Groundlings' Main Company, with Cheryl Hines, Jim Rash and Maya Rudolph. He tried stand-up comedy three times, mostly at open mic nights, but quit after being voted into the Main Company. He joined the writing teams of two failed sitcoms, including The Army Show and Action. Forte got jobs writing for 3rd Rock from the Sun and That '70s Show, two successful programs. He loved writing but had mostly given up on acting, aside from acting with the Groundlings. While performing with the troupe in 2001, he was spotted by Lorne Michaels, the creator of Saturday Night Live (SNL). Forte felt his confidence was higher than usual, as That '70s Show had been picked up for two more years. He was invited to audition for SNL, which he regarded as unexpected.  At his audition for SNL, he performed multiple original characters, including Tim Calhoun, a speed reader, a prison guard, in addition to impressions of singer Michael McDonald and actor Martin Sheen. His final character was an older piece from his days with the Groundlings, in which he portrays a gold-painted street performer who performs fellatio to pay for his face paint, which devolves into a song needlessly uttering the words "cock" and "face paint" dozens of times. He felt his time to shine as a performer was already over, as he was in his thirties when he auditioned. To his surprise, he was offered a chance to be on the show, but declined, opting instead for the financial stability of his work at That '70s Show. He felt working for SNL could not live up to the idealized version he had dreamed of, but he later realized he would be making a mistake.

Answer this question "How long did he work on that show?" by extracting the answer from the text above.
After only nine months at Letterman, he was "let go" from the job.