Who is the video for?
How will it be distributed?
What problem are you solving?
What solution is being offered?
What is the call to action?
Any video should be as long as it needs to be based on your message, no longer.
If you have more than one message to share, one approach is to create a series of 30 second acts or segments. They could stand on their own or blend together as one longer video. By focusing on streamlining each message, or 30-second act, the final production becomes easier for the viewer to follow.
If the final production falls outside predefined time limits, as with television spots, it’s easier to edit down the script than weaken the authenticity by adding filler. Final video length should never be the priority when starting a project, unless constrained by actual commercial or advertising placement rules.