Analytics Aggregates query returning empty for custom intervals

Trying to pull conversation volume for a custom time range using the Analytics API. I’m POSTing to /api/v2/analytics/conversations/queues/aggregates. The groupBy is set to interval, but the intervals array comes back empty. I’ve verified the timeFrom and timeTo are valid ISO strings. Is there a specific format required for the interval size? Here is the payload I’m sending. No 4xx errors, just no data.