monoclechris

You need a VMS. There are many to choose from, but I made this one: https://monoclesecurity.com and it's free to try for up to 4 cameras.

monoclesecurity.com is free up to 4 cameras and can record natively for h264, h265, mjpeg, mpeg4 and others. It's also extremely efficient and can record hundreds of cameras on cheap hardware.

Find a VMS that records and exposes that recording stream over RTSP playback, then use FFMPEG to grab it and write it to a file over the selected period. I *think* the FFMPEG cli is capable of this, but not 100% sure. I can recommend my own VMS from Monocle Security for this, because it support this feature, but you will have to pay for an additional 4 cameras, there may be others that are free up to 8. If FFMPEG isn't capable of doing what you need, I can modify the monocle command line interface to include your requirements.

Hi, I created Monocle Security, a company that makes a variety of CCTV related software, including a VMS. It's free for up to 4 cameras and I'm interested in finding home and commercial users alike to give it a go.

Try Monocle Security, it's my company and sounds like it might fit your requirements.