(none) - 2

It's not entirely clear. Each of the Top 3 should play 5 games against competitors. If the Top 3 plays against the Top 1 on September 23rd and loses, and is thus eliminated from the Top 3, does the next challenger come from the same group, or can a new Top 3 player step in?
Or is the Top 3 determined by the 23rd, and the winner is decided only among them?
Maybe it would be better to determine the Top 4 by a specific date and have them compete for prizes in an Olympic-style tournament: 1-4 and 2-3, with a final between the winners? In this case, the player higher in the ranking chooses the map?

Thank you for the clarification.

Starting on September 23rd:
If you are eliminated from the Top 3, you lose the right to challenge the Top 1 and 2. If you enter the Top 3, you gain the right to challenge. The Top 3 is dynamic.

Based on the initial experience, it became clear that the Top 3 players eligible for the competition (although they may be in other, lower positions in the lobby) are usually 3-4 of the same players.
The need for this condition is due to the problem of the Top 1 player not wanting to play in the last week at all, maintaining an unrealistically high rating.

The main thing is that the Top 1 player has 5 games by September 30th, as per condition 4. Mathematically, I don't believe that someone outside the Top 3 can break into the Top 1 at the last moment, unless they are colluding with someone from the Top 3. And that would be abuse and a violation of rule 1.

For the Top 2 and 3, it doesn't really matter whether they have 5 games or not, since the prize is only for the best. But the Top 2 and 3 have a tool to provide real competition to the Top 1 in direct games. And those who are slightly behind have the motivation to get at least into the Top 3.

Added a hint in point 6:
"You can attach a screenshot to the challenge message to the Top 1 and 2, confirming your position in the Top 3 in the lobby, with the date and time."