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

Not long. If painful, asap. If only red or itchy, 2-3 days.
Not long. It is important to identify the cause of eye redness, especially if it is associated with pain and/or vision loss. Redness is often caused by dry eyes, allergies or pink eye. Other conditions can also be at work, and each responds best to early intervention. If your redness does not go away within a day, see an eye doctor. If there is also vision loss or pain, go to the doctor immeditately.