I placed a GTC limit order on a Eurodollar Calendar Spread (the option kind). It was at the midpoint between the bid and ask, and became the new best offer. Later, other orders came along, occupying the same price point (although they often drop out in the overnight session, leaving only mine). I'm wondering if I would be the first in line to have my order filled at my limit price, since I was the first one to place an order at the price. Is that how it works, and if not, on what basis is the order of order fills determined?