We CAN do <1m, but very rarely do (at least in terms of persisting and showing it). We have a feature called 'Critical Metrics' that is a separate publishing pipeline into Atlas that is shorter, simpler, hardier, and supports 10s granularity, though for a trivial minority of metrics -- our current limit is on the order of around 400K metrics per cluster, IIRC, which means that if you've got, say, 1000 nodes, we're going to limit you to 400 metrics per node that would be flowing through the Critical Metrics pipeline.

(We haven't opensourced much of the pipeline ... yet)