It's not possible to filter results from the Piano API endpoint /publisher/subscription/stats by the subscription created date.
You can try using one of the two below endpoints and filter the results by using the q parameter and the subscription ID:
/publisher/subscription/list?q=<subscription id>
/publisher/subscription/search?q=<subscription id>
You can also use the /publisher/subscription/list API to get a list of subscriptions created after a specific date by entering the desired start_date and specifying the end_date with today's date.
In addition, you should add a select_by parameter which accepts the following values: create, next_bill or last_bill.
If you use create, you can use the start_date field as a filter.
It's also possible to filter by email, like this:
/publisher/subscription/list?q=<email_address>