They do tend to announce in advance, but much closer to GO Fest. Here’s last year’s post for reference, which was posted on May 3rd, 2024:
This was posted a few weeks before the first in-person GO Fest in Sendai, Japan that happened at the end of May/early June 2024. Osaka, Japan is the first in-person GO Fest for 2025 at the end of May/early June, so I would expect the timeframe for an announcement, if there will be booths, to be around the same, early May.
And 50 reveiws a day isn’t impossible. However, it’s agreements that count towards the badge, not reviews. The badge also isn’t real-time synced to your current stats in Wayfarer, so even if someone did reach the top tier in Wayfarer, it may not be reflected yet in PoGo when GO Fest starts.