When's the best time to see Bruce Springsteen and the E Street Band?

If you're out for seriousness of purpose in support of a new album, then it's best to catch the Boss early on in the get-the-message-across phase of a tour for a disc like Wrecking Ball, his 11-song 2012 salvo on the human costs of the betrayal of the American dream that he supported with two shows at the Wells Fargo Center in March.

But if you're looking to catch Springsteen at his loosest and most unpredictable, when the retirement-age rocker - he turns 63 this month - and his mighty musical compadres are at their most joyously and defiantly life-affirming, it's best to target one of the open-air summertime shows like the two that took place at Citizens Bank Park in South Philadelphia on Sunday and Monday.

That's when the set lists bust wide open, and, though staunch Wrecking Ball tunes like the defiant title track and angry, empathic "We Take Care of Our Own" still anchor the evening, the shows keep getting longer and longer, making room for the Boss and his marvelously versatile band to instinctively draw on the full range of his four-decade oeuvre, and the history of the rest of rock-and-roll besides.

On Sunday night, in a nearly four-hour show that this critic regrettably missed due to a competing musical event up Broad Street called Made in America, Springsteen was by all accounts in a wildly playful, even goofy mood, as indicated by the hot fun-in-the-summertime song titles "Hungry Heart," "Out in the Street," and covers of "Summertime Blues" and "Good Rockin' Tonight."

Monday, however, was Labor Day, and a gray, miserable one at that. And Springsteen was clearly in no mood to mark the traditional end of the summer idyll and the beginning in earnest of what's sure to be a bitterly contested presidential election by goofing around.

Instead, he started off with only an acoustic guitar, singing a solo version of "Factory," his minor masterpiece about how a lack of meaningful work deadens the soul from 1978's Darkness on the Edge of Town, the serious-as-your-life album from which all his subsequent work springs.

He followed that with not one, but four more searing Darkness songs - "Adam Raised a Cain," "Streets of Fire," "Prove it All Night" (featuring a roiling guitar tangle with Nils Lofgren), and "Something in the Night."

It wasn't until after the two aforementioned Wrecking Ball tracks and the anti-corporate-raider Celtic stomp "Death to My Home Town," in fact, that Springsteen even cracked a smile. And that was during an introduction to the gospel spirit-lifter "My City of Ruins," while he addressed the crowd in preacherly tones: "Philly, Philly, Philly, Philly! We're going to make you sweat tonight. We're going to make you work on Labor Day!"

It was also during that intro that Springsteen incorrectly referred to the building shown being demolished in a video clip as the Spectrum, when, in fact, it showed the destruction of Veterans Stadium. You're not perfect, Bruce. But as it was a way into a beautifully phrased spoken interlude about the ghosts we all live with as we age and how "they reveal to us the value of life, the preciousness of time, and the necessity of love," all is forgiven.

From there, things started to lighten up a bit, with a blast from the past in "Spirit in the Night" from 1973's Greetings From Asbury Park N.J. That song was imaginatively arranged to showcase the soloing skills of saxophonist Jake Clemons, nephew of Springsteen's longtime Big Man, Clarence Clemons, who died in 2011.

Also on display were Springsteen's limber vocals, especially impressive in the upper register on the second night in a row of holding forth with reckless abandon that most rock front men not half his age wouldn't dare attempt to match for one hour, let alone nearly four.

It was a focused and fixated night for Springsteen, who stuck with Greetings, an album that helped him find a large audience in Philadelphia before anywhere else, a double shot of the winningly verbose "Does This Bus Stop at 82nd Street?" and "It's Hard to Be a Saint in the City," which was loaded up with a dose of Darkness-style urban blues guitar firepower.

And what happened after that, other than the lovely melodic lilt of the never-played-in-Philadelphia-before rarity "Frankie," which was being played as this edition went to deadline? Did Eddie Vedder of Pearl Jam, who played at Made in America the night before and who was watching from a Citizens Bank suite, come out to sing PJ's "Better Man" with Bruce, as he has in the past? Did "Rosalita" come out to play tonight, as she did at Citizens Bank Park - where the sound was superb, by the way - the night before? For the answers to these and other questions, read my blog Tuesday morning at www.philly.com/inthemix.