Dart/Flutter Yield state after timer

I am using flutter_bloc and I am not sure how to yield state from within a callback. Am trying to start timer and return a new state after a pause. Reason I am using a timer is to get the ability to cancel previous timer so it always returns a new state after an idle state.

@override
  Stream<VerseState> mapEventToState(
    VerseEvent event,
  ) async* {
if (event is ABCEvent) {
Timer(const Duration(seconds: 3), () {
        print("Here");
        _onTimerEnd(); // adding yield here returns an error.
      })
}

Stream<XYZState> _onTimerEnd() async* {
    print("Yielding a state");
    yield myNewState();
  }

I can see that the code is getting inside the timer callback as I can see the print statements in the callback but not in the timerEnd() method.