Ad sets and ads exit the learning phase once campaigns have received around 50 optimisation events. We estimate this as being around 1-2 weeks. During this time it is important that we do not make any large edits as this will cause the learning phase to start again.
It is important to note that campaigns will go back into the learning phase if you make any significant edits. As of 2021 you can now update images without triggering the learning phase.