Hi @lukGWF - I just created a pyjls entry point extract that hopefully does exactly what you want. See the source code at extract.py.
First, you need to update pyjls:
python -m pip install -U pyjls
You can use with relative times like this:
python -m pyjls extract --start 10s --duration 5s .\20240307_141803.jls .\out.jls
Or with absolute times:
python -m pyjls extract --start 20240307T141820Z --stop 20240307T141830Z .\20240307_141803.jls .\out.jls
Does this work for you?