Sure you can use black video as long as it fits the concept and the story.
Did you ever watch 'The Shield'?
There it works.
But there are always different solutions to a question like this.
Using titles saying '45 minutes later/earlier' is a proven solution, but does it fit a 'found footage project like the Blair Witch' concept like yours?
Using timelapse is another solution, but does it fit your handheld project?
(Could be used if the camera fell down or was put down.)
Crossfading or speeding up a clock... does it fit the concept?
Shooting footage by accident can also work: walking with the camera pointing to the ground (my dad did this a few times with his vacation-videos: he thought he turned it off).
Use the passing time to build your characters with short scenes is a way to make time pass, but it takes some real time from the viewer as well.
Black video can be used in a few ways:
cut to black and cut back to image.
Fade to black and back.
Really ending the shot, pointing to the ground (maybe even put the lensthing (to protect the lens) on it). Start next shot with sound only, removing the 'lensthing' and search and focus.
How long the black video has to stay, depends on the flow and how much tension you try to build.
But sometimes (or even most times) you don't need it at all.
We all know time can and will pass between scenes: we aren't watching '24', right?
Off-topic:
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Miramax spend tens of thousands of dollars to fix it up for theaters. Miramax has been financially struggling in recent years.
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There is no relation between these two facts.
They made a lot of profit with The Blair Witch Project.
It's like saying that MGM spent millions on Ben Hur and went broke last year.
