I'll analyze the Standard winrates from the World Championship 31 Day 1 and Day 2. Let me gather the tournament data.
I don't have sufficient tournament data to answer this question. The database does not contain results from the Magic: The Gathering World Championship 31. The available Standard tournament data consists primarily of MTGO Challenges and Melee events, but does not include World Championship events.
To get the Day 1 and Day 2 Standard winrate data you're looking for, you would need to check the official Magic coverage pages or tournament results from Wizards of the Coast directly.
Sources: Searched tournament database for World Championship events; no matching records found in the Standard format dataset covering 2024-2025.