Substrate And Cycle

Hi, couple of questions - just starting a 125 litre tank, can I wash some sand substrate and leave it in the tank (without water) for a while say 2 weeks without there being any problems (tank is under stairs, and is shady, temp is about 25) ?Also building on from that, could I setup the tank fully (adding live plants) turn on the filter and heater and get the cycle going, but after about 1 week turn off electric (going away for 4 days) and resume cycle when back. Would tank be okay to continue without any probs?