First, make sure you are using the elasticsearch search engine. You can't run this kind of query on the database search engine.

Then, you want to use a range query: https://www.elastic.co/guide/en/elasticsearch/reference/current/query-dsl-range-query.html

You want to build your query string. This is a query string that gives you all the users between the two insertInstants on the user object (inclusive):

{ "range": { "insertInstant": { "gte": 1592231314000, "lte": 1592231315735 } } }

Omit the gte key if you only want users before a certain time.

Next is to turn it into an API call against the user search API, which means escaping the query's json and turning it into a JSON object suitable for FusionAuth to parse:

curl -XPOST -H 'Content-type: application/json' -H "Authorization: $API_KEY" 'https://HOSTNAME/api/user/search?' -d ' { "search" : { "query" : "{\"range\" : { \"insertInstant\" : { \"gte\" : 1592231314000, \"lte\" : 1592231315735}} }"}}'

Finally, after testing to make sure you're getting the users back you want, you can run the bulk delete API, as documented here: https://fusionauth.io/docs/v1/tech/apis/users#bulk-delete-users

Tested with Elasticsearch 7.

You can use the admin ui to build the query string.

Definitely test it out with the search first, and then use the bulk delete api.

Here's a shell script that searches for all users except one:

curl -vvv -XGET -H "Authorization: $API_KEY" 'http://localhost:9011/api/user/search/?queryString=NOT%20email:test%40example.com'

Note that I had to escape the space and the @ sign, but here's the elasticsearch query without the escaping: NOT email:test@example.com.

Also, if you are using the database search engine, the syntax will be entirely different, as this example relies on the Elasticsearch syntax.