Neil Young and Stephen Stills met in 1965, at the Fourth Dimension in Thunder Bay, Ontario. Young was there with the Squires, a Winnipeg group he had been leading since February 1963, and Stills was on tour with The Company, a spin-off from the Au Go Go Singers. When Stills' band broke up at the end of that tour, he moved to the West Coast, where he worked as a session musician and auditioned unsuccessfully for, among other bands, the Monkees. Told by record producer Barry Friedman there would be work available if he could assemble a band, Stills invited fellow Au Go Go Singers alumnus Richie Furay and former Squires bass player Ken Koblun to come join him in California. Both agreed, although Koblun chose to leave before very long and joined the group 3's a Crowd.  In early 1966 in Toronto, Young met Bruce Palmer, a Canadian who was playing bass for a group called the Mynah Birds. In need of a lead guitarist, Palmer invited Young to join the group, and Young accepted. The Mynah Birds were set to record an album for Motown Records when their singer Ricky James Matthews--James Ambrose Johnson, Jr., later known as Rick James--was tracked down and arrested by the U.S. Navy for being AWOL. With their record deal canceled, Young and Palmer headed for Los Angeles, where they encountered Stills.  Drummer Dewey Martin, who had played with garage rock group the Standells and country artists such as Patsy Cline and the Dillards, joined at the suggestion of the Byrds' manager, Jim Dickson. The group's name was taken from a brand of steamroller made by the Buffalo-Springfield Roller Company. The new group debuted on April 11, 1966, at The Troubadour in Hollywood. A few days later, they began a short tour of California as the opening act for the Dillards and the Byrds.

Answer this question "When did they make their debut?" by extracting the answer from the text above.
The new group debuted on April 11, 1966, at The Troubadour in Hollywood.