index=_internal source=*splunkd.log* host=<all indexer hosts> bucketreplicator full earliest=-15m | stats count dc(host) as num_indexer_blocked_by_peer by peer | where num_indexer_blocked_by_peer > 0 AND count > 0 | join type=left peer [ search index=_introspection host=<all indexer hosts> hostwide earliest=-10m | stats values(data.instance_guid) as peer by host]
Now (10.x onwards) you can find the time target blocked.
index=_internal bucketreplicator host=< all idx hosts> source=*splunkd.log* total_blocked_time_seconds | timechart max(total_blocked_time_seconds) by peer
index=_internal bucketreplicator host=< all idx hosts> source=*splunkd.log* total_blocked_time_seconds | timechart max(total_blocked_time_seconds) by bid