I usually submit the tournaments to the USCF for rating immediately after the tournament is finished, and the ratings are almost always published in under 24 hours.
Sometimes there are delays. They are usually caused when there is a tournament with several people joining the USCF (and this usually happens at the beginning of semesters only).
This also happens when players forget to renew their membership but I try hard to prevent these players from playing.
If the tournament is rated a few days late, it is no big deal at all (except in the one case I list below). USCF always rates the tournament once to provide a "Weekly Updated Rating" and then at the end of the month they rerate all of the tournaments just to make sure there are no errors and that everything is rated in order.
If you ever think there is an incorrect result published, notify the tournament director or organizer. They will then forward the required information to the USCF. They USCF makes corrections very quickly.
The USCF does an excellent job of rating tournaments and adjusting them properly. So even if there is a mistake made, they will add the points later.
Ratings are rarely important. They are only important for kids who are the top players in the country for their age group and they are trying to qualify for a special event and there is a deadline involved.
Also note that kids are usually very underrated. One reason this happens is because so many young players join the USCF. For example, a Kindergartner joins the USCF and gets a rating of 100. He stays around 100 for 20 tournaments. Then when he is in 1st grade, he is MUCH better at chess because he is so much more mature. And his rating is still 100. This is just an example of how kids can be very underrated and you should not treat ratings too seriously.
The USCF has a FAQ section about ratings: http://www.uschess.org/msa/FAQ.php