When i was at Cape Canaveral a while back the launch of a shuttle was delayed right up until evening time as it was a bit windy, found out later that week from the official at the base whilst on tour, in the guys words, take off isn't a problem as it will go up even in a hurricane, it's if anything went wrong and they had to glide back down, as it is unpowered then the wind creates a problem. In a way i was glad it was delayed till dark as it was such an awesome sight seeing it light up the whole sky and area as if it was almost daylight. I can just imagine how awesome a sight the Saturn 5's would have been on takeoff actually being there.