In RxJS 5+ you can do it like this
import { Observable } from "rxjs/Observable";
import { of } from "rxjs/observable/of";
import { delay } from "rxjs/operators";
fakeObservable = of('dummy').pipe(delay(5000));
In RxJS 6+
import { of } from "rxjs";
import { delay } from "rxjs/operators";
fakeObservable = of('dummy').pipe(delay(5000));
If you want to delay each emitted value try
from([1, 2, 3]).pipe(concatMap(item => of(item).pipe(delay(1000))));