Not at all: it is a provisional classification that evolves throughout the week. The medals are awarded at the end of the challenge. So you have to be first of a challenge at the end date (Monday night at 23:59:59) to win 4000 medals.
I may read the explanations but I don't really understand everything.... If we are 2 days in a row 1st at the weekly challenge of a game, does that mean that at the end of these 2 days we win 8,000 medals (4,000 per day if I understood correctly)?
Thank you for your answers and have a good evening.