They have to surpass Magnus on the list for at least 30 days.
If Magnus is not in the list then he is surpassed, as long as the list still exists.
The list appears to be updated very frequently.
No end date.
@Ernie That's the official FIDE rating list. Official FIDE ratings are updated monthly. (I'm not sure about processing time) So "at least 30 days" is a weird criteria. Is it affected by processing delays? The fact that February is 28 days?
@Ernie Also, the "January 2024" list is based on tournaments which are in December 2023 or earlier. This would count as 2023, regardless of publication delays, correct?
@DanielTilkin I checked way back machine for one older version of the page from about a week prior and it had changed. I didn't look further but from that assumed it changes somewhat frequently. If you have sure info about that, it's useful.
What I mean by that clause is that it's not just momentarily passing him. If updates are once monthly I'll wait for at least one update where he's again not the top. The point is, to identify the moment when his rating dominance is seriously over
@DanielTilkin resolving based on the invisible time when an event happened, where official rating updates aren't published til much later, seems somewhat risky and complex. I was hoping to be able to refer to the page linked and find the first time he was not first, such that he was still not first 30 days later either. Then, the date he lost first place would be considered the time he was official surpassed
@Ernie Per https://handbook.fide.com/chapter/B022022:
7.1 On the first day of each month, FIDE shall prepare a list which incorporates all rated play during the rating period into the previous list. This shall be done using the rating system formula.
The list at https://ratings.fide.com/ is just the top players from the monthly list.
@Ernie So are you sticking with the '30 day' criteria as in the description? (Which would mean that - unless FIDE changes the publication schedule - any list but the February one would count?)