Inconsistent behaviour after viewport resize

I have a couple of scenarios that have multiple viewports, sometimes it captures them after the resize a little too fast not giving the CSS enough time to be repainted. Sometimes it doesn't, but it happens more on CI, with us using docker on all environments.

I can replicate the behaviour in the browser by manually resizing in responsive mode and see the flash that I sometimes get in the backstop failures. I've tried increasing `delay` on the scenarios to ridiculous values but it doesn't seem to apply after the viewport resize, just on the first take i.e. if I have 3 viewport definitions and a delay of 10 seconds I'd expect the capture to take ~30 seconds but it only takes 10 seconds.

Is it possible to make the `delay` apply after the viewport has been resized or should there be another option? I'm happy to submit a PR for either of these if they seem reasonable.