You should be able to, but according to that article, apparently some had trouble doing it. They had to call it in.
I see it as the same as if you placed one at night and canceled it before the open the next morning. As long as it is not open, you should be able to cancel it.
Although if they hold it closed for another 45 minutes, it will be a moot point. The market shall close, and market orders are day orders, so they shall cancel themselves out.
Wish they would open it for a little trading before the weekend.