"Does it mean I have to earn 2btc before 24 hrs or I will lose?" Yes, this is right!

But you earn a % of each dividend, so the total deposited must be bigger than this. Let's say you deposit 1 BTC, and there is alreay 1 BTC invested, so you have a 50% of the total ( 2BTC). So, in order to win, 4 BTC must be deposited during next 24hours, because you earn 50% (50% of 4 BTC is 2 BTC).