In every div2 contest we see many 'unregister' accounts to be at top coders. I know that it is difficult to know if a coder is cheater or no,but we can see the time that he made his/her account. So I think it would be a good idea,if codeforces let someone to take part in a contest after 2-3 days of registaration. What do you think? Is that silly idea,or codeforces could implement it?