Hi Ryan,
Our lead developer hunted down the REST API calls you referenced. Here's his suggestions. Please let me know if this resolves your issue.
Thanks!
Lindsay McMahon
1. It appears the request is for the metric named "threads"; however, I think "overall_threads" is what you are looking for.
2. The end date in the REST API call is 4-19-2012. I believe it was intended to be 3-31-12.
3. Our REST API is based on the UTC timezone wherease your admin metrics are based on ETC. This should only result in a minor discrepancy. If you would like to account for the timezone difference, the API range is inclusive to exclusive (by hour). We use ISO 8601 for encoding dates and times, although you have to manually account for daylight savings.