imiedietly… unless your domain is not yet verified, it might take from few hours up to 2 days
From your screen shot, it’s already validated. But it may take a while before you can access your App using the custom domain, as the SSL can take a little longer to propagate.
From my experience, once you see those two green ticks, it starts working within an hour or two.
Gracias @Uzo & @Darren_Murphy , it started to work immediately.