Review from The All-Music Guide by Sean Westergaard:

Concepts of Non-Linear Time is an album of duets recorded around the same time as Opperman's Klavierstücke sessions. As with Klavierstücke, there is a mixture of composed and improvised pieces, and the listener would be hard-pressed to determine which was which. "No Memories, Please" opens the album, with Opperman playing behind the lovely voice of Rachel Arrelano. The piano playing is beautiful, but Arrelano's vocalizing may be a bit much for some. Next up is a suite performed with violin player Robert Thompson that was almost entirely improvised, but you'd never know it. The interplay is amazing the way they each know where the other is going. It's difficult to believe that this was an improvisation. Ben Adams contributes vibes to both "Dora's Aura" and the improvised "The Walls Are Coming Down," while Marc Ziegenhagen plays Moog to Opperman's Rhodes for "Reviving Aeris," the only non-piano track besides the brief intro to "The Walls Are Coming Down" (which is about ten-seconds-worth of overdubbed Keneally voices). The remainder of the tunes are a suite entitled "California 2000" with Opperman on piano and Keneally overdubbing guitars and bass, except the exquisite piano duet of "Cruisin' w/Blink." The duets concept holds things together nicely, although the tracks with vocals seem just a bit out of place. Like Klavierstücke, this is music that is poised somewhere between classical and jazz and Opperman shows himself to be as fine an improviser as he is a composer. Not only that, but he's got the musical instincts and something of a knack for surrounding himself with talented, sympathetic players. Watch out for his next recording, with his band Special Opps.