It doesn't matter if you're eating the sausage the same day, nitrites/nitrates are not really preservatives, they are the safest way to help prevent botulism during the low, slow cooking process when little oxygen is present. Botulism thrives in anaerobic conditions between 40F and 140F. Fresh sauasge do not need nitrites or nitrates, only smoked, dried, and semi dried sausage need the botulism protection