Until September 2 at 0h00, Belgian clubs are still allowed to hire some players. Also the transfer market in England, France, the Netherlands, Spain and Denmark have the same deadline. The deadline is different in other countries.
The German clubs have to finalize their transfers on September 2 at 18h00. The clubs in Italy, Greece and Ukraine have got time until 23h00.
In some countries, the transfer market closes on August 31. This is the case in Portugal (18h00), Poland, Switzerland, Scotland and Serbia (all at midnight). The transfer market already closed in Norway and Bulgaria.
The Turkish and Russian clubs get the most time to finalize transfers. Turkish clubs can buy players until September 4 at 23h00. The Russian clubs even got time until September 6 at 22h00.
So this means Cheikhou Kouyaté still gets time until September 6 if he wants to move to a Russian club.