The best days of the week to have news releases arrive at print media are Tuesday, Wednesday and Thursday. Fridays are not as good, and Monday there is lots of buildup from over the weekend. Thus we transmit any time but schedule delivery for the best possible time. Radio is not as time sensitive.
Radio shows look for guests all hours of the day and week, and weekends are as good a time as any.
One to two week minimum, or longer if you plan a major media event. One to two possibly three weeks. The longer lead time gives you the opportunity for a second release before the event.