A series of safe replica set reconfigs must pause an unnecessary 2 seconds (a heartbeat interval) between reconfigs. The primary that receives the replSetReconfig command takes around 2 seconds to receive acknowledgement from a majority of members that they have replicated the new config. After storing a new config, the primary immediately sends a new round of heartbeat requests to all members, and these secondaries immediately fetch and install the new config upon seeing the newer configVersion. The primary, however, will only satisfy the config replication check once it has learned about the newly installed configs via heartbeat responses. Therefore, since it will take 2 seconds for the primary to send out another round of heartbeat requests after itself and other secondaries have installed the new config, it will take ~2 seconds to satisfy the config replication check. Ideally this unnecessary waiting can be eliminated.