bookmarklet.js

function copyUrlToClipboard() {
  let url = getUrlThatICareAbout();
  
  // Check the docs here, you'll need to pass in a DataTransfer object,
  // so you'll need to lookup the docs for how to create one that captures
  // the url string above.
  // https://developer.mozilla.org/en-US/docs/Web/API/Clipboard/write
  navigator.clipboard.write(/* some DataTransfer object */)
}

let delay = /* however long you want to wait, in ms */

setTimeout(copyUrlToClipboard, delay);