set onduplicate(fn) {
    this._dpL = fn;
  }
If the applyOnce() call came from the fallbackInterval,
we can assume that the election runs in the background and
not critical process is waiting for it.
When this is true, we give the other instances
more time to answer to messages in the election cycle.
This makes it less likely to elect duplicate leaders.
But also it takes longer which is not a problem because we anyway
run in the background.