Jimmy Fallon and Seth Meyers on Monday evening start several weeks of late-night broadcasts aimed at reaching summer audiences, one of TV’s smallest pools of viewership. And yet, the two hosts have a giant opportunity ahead of them.

Fallon will launch NBC’s “Tonight Show” on Monday without any regular competitors — a throwback to the days when Johnny Carson hosted the show before some media companies enlisted Arsenio Hall or Joan Rivers to try and knock him off his wee-hours throne. Jimmy Kimmel is on summer vacation, and his ABC program will rely on guest hosts for the next several weeks. Stephen Colbert is in exile, and CBS is no longer competing in late night, though it has leased two hours in the time slot to entrepreneur Byron Allen. Meyers, likewise, has no direct rival for his “Late Night” at 12:30 a.m.

Little wonder, then, that NBC has in recent weeks unveiled great bookings for both shows. Before Fallon and Meyers took an early-summer break, their programs both featured members of the New York Knicks after the team powered through to victory in the NBA Finals. Starting Monday, both late-night showcases will benefit from guests who star in “The Odyssey,” the Christopher Nolan film that opens later this week (and is distributed by the company that employs Fallon and Meyers, NBCUniversal).