If they have a couple of PCs, with IE11, and a Hikvision NVR, you can bulk download many gigabytes at a time in gigabyte chunks easily enough.
Doing it via 'clips' on Playback would be very tedious. And very slow.
In the Playback web GUI, click the 'download' icon, then in the new page select the camera in question, select the date range, execute Search.
Select all the items (tickbox at the top of the column), then, click Download and leave it while it does it.
Repeat as needed.
You will likely need to run IE11 'as administrator' for it to use the configured download destination.
Then the files can be transferred on to a big USB external drive as needed.
One downside is the non-intuitive file naming.
**edit** But a screendump of the search results screen would show date/time against file name.
But you can separate the cameras into their own folders.