gistfile1.txt

var eventAsObservable = Observable.FromEvent<PropertyChangedEventHandler, PropertyChangedEventArgs>(
              ev => this.PropertyChanged += ev,
              ev => this.PropertyChanged -= ev)
              .Where((e, b) => e.PropertyName == nameof(Text));

            eventAsObservable
                .Throttle(TimeSpan.FromMilliseconds(250))
                .Subscribe(e =>
                {
                    //do stuff
                });

Use FromEventPattern() – we have the same weird 'mismatches' in Unity, because there are similarly named extension Methods.