cloudflare-worker-delay.js

addEventListener('fetch', (event) => {
  event.respondWith(handleRequest(event.request))
})

const sleep = ms => new Promise(r => setTimeout(r, ms));

async function handleRequest(request) {
  const url = new URL(request.url)

  // Disallow crawlers
  if (url.pathname === '/robots.txt') {
    return new Response('User-agent: *\nDisallow: /', { status: 200 })
  }

  const qs = url.search
    .slice(1)
    .split('&')
    .map((x) => x.split('='))
    .reduce((acc, [k, v]) => {
      acc[k] = v
      return acc
    }, {})

  const shouldTransform = qs.path && qs.delay;

  if (!shouldTransform) {
    return new Response('...')
  }
  const newUrl = `https://${decodeURIComponent(qs.path)}`;
  const res = await fetch(newUrl)
  const response = new Response(res.body, res);
  response.headers.set('cache-control', 'no-store');
  await sleep(qs.delay);
  return response;
}

Usage:

https://delay.cpclermont.workers.dev?path=$urlWithoutProtocol&delay=$delayInMs

Example:
https://delay.cpclermont.worker.dev?path=via.placeholder.com/150&delay=3000