Vortex Media's Timelapse Calculator can be used in two ways:

1) Find out what the final duration of a clip will be with the settings you have chosen.
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2) Find out how long it will take to shoot a timelapse with the settings you have chosen.
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Glossary:

Clip Length: The total running time of the timelapse clip that will be recorded.

Interval: The elapsed time on the clock between captures.

Event Duration: The total time on the clock that the camera must be up and running to record the timelapse.

Format: The video format that your camera is currently set on: 30P, 24P, 25P, 60i, 50i.

Frames: The number of frames that are recorded during each capture. Usually you will want to leave this set on "1".