The one second delay for non-amp compliant ads is to ensure a quality reading experience. AMP ads are server side fetched and validated to not require subsequent client side loading. Non-amp ads have no such restrictions and can cause jank as they load, which the AMP experience is trying to avoid by delaying them a bit.

More here: https://wptavern.com/amp-has-irreparably-damaged-publishers-trust-in-google-led-initiatives