it's 5 and 7 days for the achievement. a day in DR is 2 hours of playtime, so 10 and 14 hours respectively. i plan on trying it someday. a guy i know completed it and said it wasn't that hard. you basically get all 3 food books, get the rest of your inventory full of food and go back to the security room. there you wait til your health's at 1 block, then eat an item. the way he described it you only have to do some surviving for a limited time
i don't think you have to make the most out of the frozen/raw stuff, since there are people who have survived 17 days