Well, this toon has 8 hours of amps right now, so not really an appropriate measure, but, with the amps, Seismic/Earth clocked in under 2:00. I imagine it would fall in line with some of my other blasters in the 2:00-2:30 range without them.
Run 1 - 1:45
Run 2 - 1:53
Run 3 - 1:52
Chain is Entomb -> Tombstone -> Heavy Mallet -> Seismic Smash, playing with tossing Upthrust in there periodically for its multiple -res procs, but not sure how much those are helping at only a ~30% proc rate.