Wait source for no more then 20ms, if it fails -- retry 3 times. Example for https://stackoverflow.com/questions/55206845/rxjs-wait-on-value-from-observable-if-it-doesnt-come-after-a-specified-time-p

index.js

const { rxObserver, palette } = require('api/v0.3');
const { of, timer } = require('rxjs');
const { retry, switchMap, timeout } = require('rxjs/operators');

let index = 0;
const source$ = of(void 0).pipe(
    switchMap(()=>
      // 4 attempts
      timer([20, 20, 20, 5][index++])
    )
  );


const retry$ = source$.pipe(
  timeout(10),
  retry(3)
);
  
retry$.subscribe(rxObserver());

Run at https://observable-playground.github.io/gist/c526cd7d75713adbf86b60db5860e333