You got me, I actually searched for evidence that the <blink> element supported ...

You got me, I actually searched for evidence that the <blink> element supported a `speed` attribute.

The MDN page about <blink> has example CSS to make the element blink again. If you wanted to make speed variants, you could use CSS selectors that set different durations based on a data attribute and its value:

  blink {
    animation: 2s linear infinite condemned_blink_effect;
  }

  blink[data-speed: fast] { animation-duration: 1s }
  blink[data-speed: slow] { animation-duration: 4s }