When Bruce Springsteen and the E Street Band performed at the Izod Center in the New Jersey Meadowlands on May 21, there was one musician conspicuously absent: Max Weinberg, the group’s drummer for more than three decades.

As Mr. Springsteen tore into his opening number, “Badlands,” Mr. Weinberg was on another stage 3,000 miles away, pounding his drum kit through a dress rehearsal of “The Tonight Show With Conan O’Brien,” in advance of its debut last Monday on NBC. The following night Mr. Weinberg boarded a red eye for the East Coast so he could rejoin his E Street band mates, however temporarily, for the second show of that New Jersey stand, which fell on a rare night off from his new duties.

For Mr. Weinberg and the seven other East Coast musicians who have relocated to California along with Mr. O’Brien  including all the founding members of the Max Weinberg 7, the house band on Mr. O’Brien’s “Late Night” for 16 years  the turnover in hosts (and bands) on “Tonight” has proved to be both exhilarating and disruptive.

No one has had to make a more prominent transition than Mr. Weinberg, who was replaced that first night in New Jersey by his son, Jay, 18, who is also substituting for his father on at least the first seven dates that Mr. Springsteen is playing in Europe, on a leg of the tour that began last Saturday in the Netherlands. While Mr. O’Brien and NBC had previously permitted Mr. Weinberg to take leaves of absence from “Late Night” for as many as six months to tour with Mr. Springsteen, the opening weeks of “Tonight” were ultimately deemed too important for him to miss.