How long does it take for an AdMob Ad unit ID to become active?

Question

I created a new Ad unit ID around 4 hours ago and started using it in the release build of my unreleased Android app. But all I get is a blank view and the following logcat

Answer 1

Sometimes the Ad Unit ID starts delivering ads immediately, and sometimes the Ad Unit ID can take a few hours before delivering ads. There is no official AdMob documentation stating the activation time.