There are lots of group buys for miners with delivery date somewhere next year. But according to these calculations even a couple of weeks matter http://www.vnbitcoin.org/bitcoincalculator.php

Is there something I don't understand, or most people doesn't know about difficulty growing? Or everybody who takes part in group buys for Q1/Q2 miners believes that bitcoin also going to grow with difficulty increase? The last month of Q2 is June, what if miners won't be delivered until then?