I chose two different options. If I feel the video really strengthens the lesson, then we'll watch it during lesson time. If I feel that it's more supplemental, then we'll watch it during spare hours.
For example, when we were studying European countries in geography, I would order Rick Steves videos from the library. We would watch these during our spare hours to get a better look at the countries we were studying. On the other hand, when we studied early American history, I had a video on Plimouth that showed how the area was set up, what the houses would have looked like, etc. We watched that video during regular lesson hours.