How long can I wait with foot redness to see if it goes away without seeing a doctor?

Extent? Pain? If it infection it is best to see physician early because walking will become difficult.Redness can be sign of infection, trauma, allergic reaction and needs to be seen to determine appropriate treatment.
Get diagnosis first. Hi, it’s hard to say without a picture but there is a great app that may be able to help you get a diagnosis without being seen in person by a dermatologist. The app is called VisualDX and is one of the best, if not the best out there. Many clinicians, including myself, use it. Just snap a photo and it gives you a list of possible diagnoses. Good luck!
Not long. It is usually a sign of infection or inflammatory arthritis (gout, for example). It is very important to treat either quickly to prevent long term problems.