With this app you are able to calculate the required recording duration for your timelapse videos.
You can enter the desired video duration, the resulting video FPS (frames per seconds) and the shutter interval and the app will make the calculation for you.
You can also calculate the duration of a timelapse video based on the recording duration, intervall and FPS settings.

The app is free, but inside you have the option to donate a small amount of money, so the developer can buy an ice-tea. Thanks!