You don’t have to wait more than around 30 seconds. There’s no requirement of duration of your disability going backwards. There only is a requirement that you be disabled looking forward. In other words, you will have to show that you have a disability that has lasted or is likely to last at least 12 months. If you meet that criteria, and very often you would know that immediately upon suffering the disability, the impairment that you’re suffering from. If you believe and your doctor will testify, or affirm that you’re going to be disabled for at least 12 months, you should be applying. Do not wait, go out and file.