Wait an hour after eating?

I have read that if you have something “sugary” that if you don’t wait an hour to brush you may do a lot of damage to your enamel and I have some questions.

How sugary is “sugary”? If I eat breakfast cereal and milk is that sugary enough that you have to wait?

Is this advise that should just be followed no matter what you eat or is there really a sugar threshold that should be considered?

Does bread count as sugar for this warning since it has a lot of carbs?

Is an hour enough or does it vary? Is an hour said because that is actually a little longer than needed or in some cases is an hour less than ideal time?