I got a reply from Apple Support:
To protect customer privacy, Apple shows App Analytics data only when a certain number of data points are available. The data is aggregated so that customers can remain anonymous.
As soon as there are enough data points to show, you'll see your App Analytics data.
This brings 0 bits of new information to the table, it's what we all suspected anyway and it's what any AI would say on this question.
I need to know more precisely when the analytics appears. At least to do some planning and give estimates to myself and my clients. I would continue begging them for information. This would be especially important soon, because Trends would be removed – currently it's the only source of information about installs & In-App Purchases.
Imagine in the future you won't be able to know anything about your app, even 2 months after release. What a torture. I now regret respecting user privacy and not installing third-party analytics.