This is a framework for alerts on HADR_SYNC_COMMIT waits in AlwaysOn AG environments. The value is in milliseconds. At default options, this will check every 30 seconds and require that the waits remain above the threshold for two polling intervals in a row before evaluating as "True" and triggering any associated response.
See https://www.sqlskills.com/help/waits/hadr_sync_commit/ for more details on this wait type.