Welcome to the Secret Laboratory of Prof. W.S.
You can use the machine in front of you to travel back in time. You will be asked for the year you want to visit, which is a 4-digit code. You obtained the first half of that code in riddle #5 and you got the second half in the roosters and rats riddle that you just completed.
Click on the machine to use it. Have a good trip and good luck.