In a cash account, the proceeds from the sale of any security will be held until settlement; for options, this is effectively overnight. One can sell an option on one day, and then use the funds the next day to purchase something else. If I attempt to purchase something with the unsettled proceeds from a sale, I am subject to the free-rider rule, which prohibits me from selling the new purchase until the first sale has settled.
In a margin account, the proceeds from the sale of stock can be used immediately to enter a new position. However, options aren't marginable. Does this affect the calculation of buying power and the free-rider rule? When I sell an option in a margin account, can I use those proceeds immediately and without restriction, or am I still limited to the buying power with which I started the day?