There’s a ton of advice out there on best practices for video length on various platforms. Here are some quick stats by platform:
Facebook (pre-recorded): 2 minutes
Facebook Live: at least 10 minutes; 15 minutes is a sweet spot
Instagram: 30 seconds
Twitter: 30-45 seconds
YouTube: 2 minutes
But stats are just that: stats. My advice is ALWAYS to explore what your own audience responds to, what works best to tell your content’s story, and, above all, what you actually want to do.