Time is running out for Jay Leno to reunite with David Letterman in late night – and right now the ball is in Leno's court. According to sources inside Late Show with David Letterman, the program has reached out to Leno about coming on as a guest before Letterman departs CBS on May 20.

We asked Leno last week in Miami at the National Association of Television Program Executives conference if he was mulling the offer. “I haven't heard that,” he said. “I'll have to check into that.”

Indeed, the request was first made a year ago, back when Leno was wrapping up his Tonight Show run. It’s unclear whether the ask ever reached Leno himself. More likely, the invite was discussed between Leno's and Letterman's producers.

A year later, Leno has been busy performing standup around the country and working on his cars (including for CNBC's upcoming Jay Leno's Garage). But with just four months left before Letterman retires from Late Show, producers are expected to renew the request in order to get Leno on the show before then.

Such a reunion would be historic in the annals of late night history – and probably a big audience draw. Leno and Letterman previously reunited, with Oprah Winfrey in the middle, for a Late Show Super Bowl ad on CBS in 2010.

But the last time Leno appeared as a guest on Letterman’s show was May 7, 1992 – three weeks before the debut of The Tonight Show with Jay Leno. Leno has never been on Letterman’s CBS show, and Letterman never appeared on Leno’s Tonight Show.

Leno was one of Letterman’s favorite comedian guests during the run of NBC’s Late Night with David Letterman in the 1980s. That all changed after NBC picked Leno over Letterman to replace Johnny Carson as host of The Tonight Show. The rift that developed between the two has been well documented.

But now that the so-called “late night wars” have faded into the sunset, it may be time for these two estranged friends to meet up one more time after dark.

Last year, Leno told us that he was open to visiting Letterman on the Late Show: “That could happen, why not,” he said while conducting an interview about the end of his Tonight Show reign. “It's certainly a possibility. Some of my best moments were doing the show with Dave.”

In the interview, Leno said he didn’t expect to renew his relationship with Letterman, even though they would no longer be in direct competition: “It’s the same. I don’t think it changes anything.”

But he also went on to recount some of his fond memories of appearing on Late Night with David Letterman.

“The real trick to being a comedian is finding that perfect audience. Seinfeld is a perfect audience, as I am with him, and Letterman is too,” Leno said. “With Dave it was never about the joke, it was the joke-on-the-way-to-the-joke that always would get the laugh. Dave would always laugh. I remember talking to Dave once and saying, ‘You know, Dave, I was out in California, out at the old Manson place,’ and Dave would go, ‘The old Manson place!’ And I’d say, ‘Oh yeah, the old Manson place!’ I knew he would think that was funny and he did.

“When you know another person and you know what makes them tick, you know what’s going to work. With Dave, whenever I would do his show it was one of those simpatico deals. Dave is a nervous person. So whenever I would do his show I would walk out with a huge meatball sandwich and I would eat it. And Dave could not eat hours before the show. Maybe he'd have soup at noon. So I would go out with the sandwich and offer him some. It was just fun, he was like, ‘How can you eat and be out here?’ It was just so different for him.

“So it was fun to know what makes the other person laugh. Great fun. So I wouldn't rule it out.”