在redux-observable中，如何在运行完成时测量epics持续时间？

import { timer } from 'rxjs';
import { tap } from 'rxjs/operators';

import { ofType } from 'redux-observable';
import { timer } from 'rxjs';
import { tap } from 'rxjs/operators';

const myEpic = (action$, state$) =>
  action$.pipe(
    ofType('MY_ACTION'),
    tap(() => {
      // 开始计时
      const startTime = Date.now();

      // 在epic完成时触发
      timer(0).pipe(
        tap(() => {
          // 计算持续时间
          const duration = Date.now() - startTime;
          console.log(`Epic持续时间：${duration}ms`);
        })
      ).subscribe();
    }),
    // 其他操作
  );

import { createEpicMiddleware } from 'redux-observable';
import { createStore, applyMiddleware } from 'redux';

const epicMiddleware = createEpicMiddleware();

const store = createStore(
  rootReducer,
  applyMiddleware(epicMiddleware)
);

epicMiddleware.run(myEpic);