What's the frame rate for time lapse videos? Can I set up my own?

For time lapse video, the frame rate is preset to 25 fps and a typical frame size is around 50KB. The actual frame size varies from 20KB to 100KB depending on the target scene, camera settings, and lighting conditions. For estimation, you can use 50KB. 

I'm afraid that you can't set up your own. The frame rate for time lapse videos is fixed and cannot be changed. But you can save those photo sequences and then use them to re-edit a video with the help of a third-party video editing app.