For the sniper challenge, it's best to shoot the front tagets without using the scope; that saves a few seconds. And when the wind is low, you should only shoot the rear targets, otherwise you'll spend too much time aiming. This helped me get it done in exactly 60 secs.
darkmoth38, I had the same problem before. Out of nowhere, the controls would stick or delay.
It's because the game is running too slow in your browser. So I loaded the game in firefox and had no other tabs open. The problem went away after that.