Are the two of you using the same answer to the question "Does a X% chance of 2 events (in given interval) contribute X% or 2X% to the chance of seeing one even

Are the two of you using the same answer to the question "Does a X% chance of 2 events (in given interval) contribute X% or 2X% to the chance of seeing one event?"? That is, do you mean [time for a 50% chance of seeing ≥1 decay] or [time to see, on average, 0.5 decays].