The opLatencies section of serverStatus was added in MongoDB 3.4. These metrics are collected by FTDC, Ops Manager/Cloud Manager monitoring, and third party tools.
On an idle replica set, read latencies can be observed in the 5000ms range due to replication timeout.
This is confusing for anyone observing these metrics and they may believe there is a performance problem, solely based on these artifacts. When a steady write load is applied, these metrics even out.
Splitting oplog latencies out from this metric would prevent this confusion, but still allow diagnosis of replication issues.