Does it proc off of each tick of a HoT (such as renew, riptide, rejuv, or flash of light)?
YES
(с) http://www.wowhead.c...ments:id=893226
EDIT: I did some testing to determine the internal cool down of the trinket. The original value that I was using (0.25 seconds) was clearly wrong. From 500 data points, the shortest time between procs was 0.331 seconds. From this we can conclude that the internal cooldown is no larger than 0.33 seconds. Also, with 500 data points, it is unlikely that the internal cooldown would be significantly smaller than 0.32 seconds.
(с) http://www.wowhead.c...ments:id=916581