How can I create a batch script to JUST crop a series of time lapse photos

The affordable Elements+ add-on has a script for cropping multiple files:

roboCrop

I don't know if that fits your need.

Otherwise,

I suppose all your source files have the same dimensions.

I could imagine a way to apply the same crop to a number of photos opened at the same time in the ACR converter module. That works not only with raw files but also on jpegs, psd or tif.

The number of files you can open at the same time varies depending on the files format and size, but that works with batches of 50 to 100 jpegs.

In the ACR dialog, you click the button 'select' all. Then you use the crop tool icon on the top tool bar and you define your crop. It can be chosen from default ratios or custom. You draw and place your crop rectangle where you want, you can even tilt it.

Click 'Done' : the (lossless) crop will be applied to all files. (If you click 'Open', you'll have to save each file individually from the editor).

Then you select the whole batch in the organizer and use the 'export as new file' function to get a copy of your cropped files in a new folder.

Not for thousands of photos, but free, fast and flexible.