Can I extract dates from Elasticsearch to populate a variable?

grafana version: 9.0.2 on Linux
elasticsearch version: 7.16.2

I would like to have a dashboard variable representing the list of dates in the selected viewing range so I can repeat a panel.

I can pull easily pull times out of elastic:

but what I want is just the dates. Are there any other parameters I can add to my elasticsearch query here to control what I get back, for example only pulling out the date part?