bufferToggle

you can pass first

import { interval, fromEvent } from 'rxjs';
import { bufferToggle, mapTo } from 'rxjs/operators';

const click$ = fromEvent(document, 'click');
const opening$ = interval(3000);
const buffer$ = click$.pipe(bufferToggle(opening$, 
  // count: opening$ emit value
  count => count % 2 ? interval(500) : null // when count is is Odd emit close after 0.5s
));

// result: when opening$ emit 2(Odd), will buffer all value between now and 0.5s late    

Official Doc: rxjs.bufferToggle