Set the time of a commit

I’ve got an OAuth app that will make modifications to the contents of a repo with the following endpoint:

put /repos/{owner}/{repo}/contents/{path}

This works just fine, except, I’d like to specify the time at which the commit was made to the file.
The documentation references two parameters called author and committer. These are objects with a required name and email, but an optional time string.
I’ve tried setting the time in my request like this:

{
	"author":  {
		"name": "My Name",
		"email": "me@myemail.com",
		"date": "2020-11-14T22:21:06Z"
	},
	"committer":  {
		"name": "Seth Painter",
		"email": "me@myemail.com",
		"date": "2020-11-14T22:21:06Z"
	},
	"message": "my commit message",
	"content": "<Base64 data>"
}

I've tried using just author or committer, neither fix the issue, I've also tried the format that is used in standard git commit messages

Sat Nov 14 16:21:06 2020 -0600


But that hasn't worked either.
The documentation page doesn't provide any kind of specification for the date format. if someone could tell me how it's set that would be epic.

When I send this request, it runs fine, but the time of the commit is the current time, rather than the one I try to set.