How long does it take for vasculitis on legs and feet to clear up without medication?

It depends what. kind of vasculitis you have? Usually treated with medications such as steroids and immuno-suppressive medicines is one of them.
Depends. There are many causes of vasculitis and it would depend on what is causing your lesions. You may visit this site for information, but it would be prudent to see a doctor for an evaluation.
https://www.mayoclinic.org/diseases-conditions/vasculitis/diagnosis-treatment/drc-20363485.