Plus the X-men were traveling all around the world so the time doesnt really track. You are right in that if Storm turned on tv, Genosha wouldnt have...
His state of mind also plays into his action as he just saw Genosha massacred by a bunch of sentinels. I dont think his actions were self defense but...
From last episode it seemed like the prime sentinels would be like TWD zombies, activated upon death but as we got the backstory the programmig can ...