This feels a bit hacky, but works:

(t/format (t/formatter "HH:mm:ss") (t/+ (t/midnight) (t/new-duration 87 :seconds)))
;; => "00:01:27"

(let [duration (t/new-duration 87 :seconds)
      hours (t/hours duration)
      minutes (rem (t/minutes duration) 60)
      seconds (rem (t/seconds duration) 60)]
  (format "%02d:%02d:%02d" hours minutes seconds))
;; => "00:01:27"

ha, I have the same helper duration -> hrs,mins,secs https://github.com/dvingo/tick-util/blob/8eb28d04df664d616adab7a5779db48c1b924ead/src/main/dv/tick_util.cljc#L1421

SO seems to agree https://stackoverflow.com/questions/266825/how-to-format-a-duration-in-java-e-g-format-hmmss