The original mini-series was four hours, split in half over two nights. The Final Battle
was six hours, and split 2 hours each over three nights.
I've blocked out the memories of the television series.
I've not yet read Kenneth Johnson's V: The Second Generation
, which is a followup to the original mini-series, and doesn't take into account anything from TFB or the weekly series.
If you're prepping for the new version and have never seen any of the 80s stuff, I think you could get by just watching the original 4 hours.