The action duration is the average time it takes to perform an action expressed in standard format.
Action duration is calculated as the total time spent by visitors divided by the number of actions which have a registered duration.
Notice that the last action in a visit has no time since timestamps are only set at the beginning of each action.
An action automatically times out after 30 minutes inactivity (together with the visit). Thus, an action cannot last longer than 30 minutes.