How much MB/GB does it use to TAKE a video?

I have so crazy kids threatening to mess up my challenger. So I wanna take keep my iPhone on record all night so that if they do mess up anything I have proof. I have 4.6 GB of free space on my iPhone, will that be enough to keep my iPhone on Record for about 8hrs

Answering question 1: It depends on the compression used and the device capturing the video… And it depends on the video quality you need.

Answering question 2: No.

It depends largely on several parameters inside the video. If you record it with default iPhone camera app @ 1080p, usually that free space of yours will be entirely used for about one and half hour or less.

Why don't you try it out first, see how long would it take to fill her up?