When can I start exercising if I have plantar fasciitis?

Exercise now. You can exercise now. Practice what I call provoke and recover to maintain a level pain pattern until you get better. You will not be causing damage as long as you indeed have pf. And start stretching your calves now daily to treat the underlying cause.
TO toletance. If you truly have plantar fasciits you should seek medical attention to have this treated. Once you are under the care of a specialist you should be able to resume exercise immediatley or in a short time. You should not resume exercise until evaluated because there might be more going besides just plantar fasciitis, such as a stress fracture. Go to heelpainnow. Com for more information.
Ask your doctor. Talk to your doctor for specific treatment guidelines. Usually mild-moderate exercise can be doe to tolerance. Make sure you are doing your stretching on a consistent basis, your shoes are in good repair and have adequate arch support. In more severe cases, a period of rest might be beneficial until progress is made.