[Al Skierkiewicz]

Tom,
You reading is correct. The smaller breakers have a slightly different trip spec and the 120 amp breaker is longer still. However, all of the resettable breakers will have a shorter trip spec after the first reset as the breaker is already at an elevated temperature. This is also compromised if the breaker is in a hot environment. i.e. near a hard working motor(s) or thermal shadow, adjacent breakers are also passing a lot of current or if the wiring attached to the PD has not been properly terminated (high resistance) and is creating heat from the termination.