If we are moments away from exiting the quiet period,

we might as well claim we are in it, because otherwise we just say ¯\_(ツ)_/¯ which is less
helpful.

core/src/main/java/hudson/model/Queue.java

@@ -2487,7 +2487,7 @@ public class Queue extends ResourceController implements Saveable {
 
         public CauseOfBlockage getCauseOfBlockage() {
             long diff = timestamp.getTimeInMillis() - System.currentTimeMillis();
-            if (diff > 0)
+            if (diff >= 0)
                 return CauseOfBlockage.fromMessage(Messages._Queue_InQuietPeriod(Util.getTimeSpanString(diff)));
             else
                 return CauseOfBlockage.fromMessage(Messages._Queue_Unknown());