The Pulse qualifier activates an action output for exactly one scan cycle when the step first activates.
A "scan cycle" is one complete execution loop of the Sequence program. The pulse lasts for the duration of a single cycle, which is typically very short (milliseconds).
{GIF:HERE} - Step properties panel showing the action 'Increment counter' with qualifier dropdown set to 'P' (Pulse), no duration field visible since P requires no time parameter
from automation_machine import ActionQualifier
step.add_action("counter_increment", "Increment counter", qualifier=ActionQualifier.P)
No duration parameter is needed.