diff --git a/hub/internal/monitor/staleness.go b/hub/internal/monitor/staleness.go
index 76bf33a..2b8c7b3 100644
--- a/hub/internal/monitor/staleness.go
+++ b/hub/internal/monitor/staleness.go
@@ -22,8 +22,9 @@ type StalenessChecker struct {
 	logger    *log.Logger
 	onEvent   EventNotifyFunc
 
-	mu     sync.Mutex
-	states map[string]string // customerID → "ok" | "stale" | "down"
+	mu            sync.Mutex
+	states        map[string]string    // customerID → "ok" | "stale" | "down"
+	downtimeStart map[string]time.Time // customerID → when node first became unreachable
 }
 
 // NewStalenessChecker creates a checker and initializes state from current data.
@@ -31,12 +32,13 @@ type StalenessChecker struct {
 // onEvent is called after each hub-generated event is saved (may be nil).
 func NewStalenessChecker(s *store.Store, threshold time.Duration, onEvent EventNotifyFunc, logger *log.Logger) *StalenessChecker {
 	sc := &StalenessChecker{
-		store:     s,
-		threshold: threshold,
-		downAfter: 2 * threshold,
-		logger:    logger,
-		onEvent:   onEvent,
-		states:    make(map[string]string),
+		store:         s,
+		threshold:     threshold,
+		downAfter:     2 * threshold,
+		logger:        logger,
+		onEvent:       onEvent,
+		states:        make(map[string]string),
+		downtimeStart: make(map[string]time.Time),
 	}
 
 	// Seed states from current report timestamps — no events on init
@@ -116,13 +118,25 @@ func (sc *StalenessChecker) Check() {
 
 		// State transition — emit event
 		sc.states[c.CustomerID] = newState
-		sc.emitTransition(c.CustomerID, oldState, newState, age)
+		if newState == "stale" && oldState == "ok" {
+			// Record when node first became unreachable
+			sc.downtimeStart[c.CustomerID] = time.Now()
+		}
+		downtimeDur := age
+		if newState == "ok" {
+			if t, ok := sc.downtimeStart[c.CustomerID]; ok {
+				downtimeDur = time.Since(t)
+			}
+			delete(sc.downtimeStart, c.CustomerID)
+		}
+		sc.emitTransition(c.CustomerID, oldState, newState, downtimeDur)
 	}
 
 	// Clean up customers that no longer have reports
 	for id := range sc.states {
 		if !seen[id] {
 			delete(sc.states, id)
+			delete(sc.downtimeStart, id)
 		}
 	}
 }