In each Clip-thumbnail there is showed a time, like in this one, which says 7h26m57s. What does this mean exactly ? This clip does not consist of 7h26m video recording, so it must mean something else I guess.
Keep in mind a clip is not an alert. Alerts are triggered events, usually motion, and typically a few seconds but can run much longer depending on the duration of the trigger event. A clip is a section of continuous recording and does contain the alert video as well. Alerts are just "location markers" in a continuous record file.