IMO flying 7 straight nights and flying every night is safer than flying 3 days and then 3 nights, or vice versa. I find it far easier to fly nights if I stay on nights, and let my body adjust to that. I spent a number of years flying nights full time, and I far prefer that to rotating between days and nights. Constantly changing one's circadian rhythm is tiring and in the long run, dangerous in several ways.