Angular 2 clock with RxJS Observable
Your service looks perfectly fine to me. As far as the Clock component goes, I can only recommend one thing.

When getClock().subscribe(...) is executed, a reference to the subscription is being returned back. Ideally, the reference should be kept as long as the component is alive. On component destruction, the subscription should be released by invoking subscription.unsubscribe().

@Component({
  selector: 'clock',
  templateUrl: './clock.component.html',
  styleUrls: ['./clock.component.css']
})
export class Clock implements OnInit, OnDestroy {

  private _clockSubscription: Subscription;
  time: Date;

  constructor(private clockService: ClockService) { }

  ngOnInit(): void {
    this._clockSubscription = this.clockService.getClock().subscribe(time =&gt; this.time = time);
  }

  ngOnDestroy(): void {
    this._clockSubscription.unsubscribe();
  }

}


P.S. As a minor side note, I want to mention that some devs like to explicitly mention the OnInit/OnDestroy/... interfaces in the class' implements clause. I am not sure whether it's very helpful or a big deal, but at least the compiler will complain if the ngOnInit is missing while class declares that OnInit is implemented.