They say tragedy plus time equals comedy. There’s a lesser-known musical corollary as well: disposability plus time equals quality. Eventually silly pop songs assume the consequence of longevity — early Beatles and Michael Jackson, for example, or the latter-day canonization of the bubblegum pop of the 1950s. Echoes of that era’s doo-wop style show up on breakout single “Baby,’’ from 16-year-old Canadian heartthrob Justin Bieber’s latest album. Hip-hop is here, too, with guest star Ludacris’s goofy cameo. It effects a musical anachronism, albeit a catchy one, but in this sped-up recycling moment all styles all at once are grist for the mill. Sultry reggaeton is repackaged here for the tween set with Sean Kingston’s “Eenie Meenie.’’ “Shorty’’ was never sung so literally. On songs like the bluesy “U Smile’’ and the Jackson Five disco groove of “Runaway Love,’’ Bieber is poised beyond his demographic, compelling even. The incubation period for graduation to respectability has shortened (wizened elder statesmen like Justin Timberlake and Usher, both Bieber fans, come to mind), but will anyone care about this record of au courant R&B, soul, and junior high pop five minutes into the future? Give it some time.