Insulin is an urgent need for any T1 diabetic. They could maybe make it a week depending on what they ate, but they could also be dead in a day. There isn't really such a thing as mild or severe Type 1, only well treated and poorly treated.

You could maybe say "insulin is an urgent need for a diabetic who just ate 3 cookies, but not as urgent for one who just ate a plate of vegetables". But both will need some amount of insulin within 24 hours.

Type 2 is a different story, and not all Type 2's need insulin.