Andy, the script I offered is an attempt to give you a template for customizing to your needs.
That script incorporates the date and time stamp in the video with the ffmpeg's "drawtext" option string (that is composed of other parameters which I've explicitly defined as parameters, to make it easier to understand).
The "--duration" option is my suggested approach for giving a length of the recording time (using hours), which is then converted into the value for ffmpeg's "-t" option which is in seconds.
But all of that can be changed by yourself, if you prefer to work with minutes, and modify the calculations in the script accordingly. If you want me to change that to minutes (i.e. 720 minutes for a 12 hour recording), I can modify my script for that, if you prefer.
I backed away from specifying start and end times because it got a bit too complicated for me. That is why I only offered a parameter for wait, in minutes, before the recording starts for the specified duration.
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Please see my later posting for the finalized script.
"--duration" was replaced by the two mutually-exclusive options "--hours" and "--minutes".