How long can a video be (maximum length) to be able to upload to Facebook? (240 minutes)
Technically, it's 240 minutes, but your video is probably a lot shorter than that. The problem is the file size is too large, because your phone camera (or whatever you're using to record video) is on a very high resolution setting. Turn down the resolution of your recordings, and try again. Or upload your video to Youtube, then download from there, since Youtube will automatically compress your video for you.