What's the earliest a market maker can cancel a stop-loss order on his own?

I bought stock in February (USO) and put in a stop loss to protect my profit. I then notice the stop loss was cancelled by the market-maker 6 months later. I am assuming this 6 month period is somewhat standard. But what’s the earliest you’ve heard of these contracts being cancelled by the market maker? luckily the stock I bought kept going up, so i put in a new stop-loss