Update BBS metrics docs
| `MigrationDuration` | Time the BBS took to run migrations against its persistence store. Emitted each time a BBS becomes the active master. | ns |
| `OpenFileDescriptors` | Current (non-cumulative) number of open file descriptors held by the BBS. Emitted periodically. | number |
| `RequestCount` | Cumulative number of requests the BBS has handled through its API. Emitted periodically. | number |
-| `RequestLatency` | Time the BBS took to handle requests to its API endpoints. Emitted periodically. | ns |
+| `RequestLatency` | Maximum amount of time the BBS took to handle a request to one its API endpoints over a 60-second interval. Emitted every 60 seconds. | ns |
| `TasksCompleted` | Total number of Tasks that have completed. Emitted periodically. | number |
| `TasksPending` | Total number of Tasks that have not yet been placed on a cell. Emitted periodically. | number |
| `TasksResolving` | Total number of Tasks locked for deletion. Emitted periodically. | number |
