I've used my MP number on a couple CO flights and they seem to post with the same timing as UA flights (i think fridays?). Bonus miles, too. Pretty seamless so far for me.
No, they don't just post on Fridays. UA flight mileage usually posts to my account within 1-2 days. CO flight mileage has consistently posted to my UA account 3 days after the flight. Of course, YMMV.