@Override
    public long getDelay(TimeUnit unit) {
      return unit.convert(this.whenToExpire - EnvironmentEdgeManager.currentTime(),
        TimeUnit.MILLISECONDS);
    }
@param when When to expire, when to come up out of the queue. Specify in milliseconds. This
            method adds EnvironmentEdgeManager.currentTime() to whatever you pass.
@return This.
hbase-server/src/main/java/org/apache/hadoop/hbase/regionserver/MemStoreFlusher.java