API Patch to Replace Date Field from Another Date Field Value

I'm having an issue when patching a date custom attribute value to another date custom attribute. Every way I've tried returns a "200 ok" status, but the target attribute remains blank. 

Here is an example of one test. End Date is populated but attribute 2479 remains blank. I have tried appending the time and time zones to the value, but still no luck even though I receive no errors.
[

{"op": "replace", "path": "/attributes/2479", "value": "{{End Date}}"}
]