Based on our recent experience with BI connector refresh , we had to bump the sample size to 15000 recently. This contributed to a longer outage on our real-time dashboard reporting. It took more than an hour for the schema refresh to complete. We are hoping in future we can add couple features to Mongo Atlas :
1) when BI connector refresh runs it would consider documents based on the last update time in the sample, so we can bring down the volume of sample considered and reduce the down time.
2) Enable BI connector schema refresh at a collection level within Mongo Atlas.

For additional details , please check the ticket - 00808543