your credit score can (and most of the time will) change every single day... I used to do a soft pull on my credit with scores every day.. and sure enough.. the scores would change..
Here's the scoop....
there are THREE credit reporting agencies.... Experian, Equifax and Transunion.
you have a score for each of these three agencies.. however, they just announced a few months ago that they are ALL going to use the same "credit scoring model" (before they would just each have their own scoring system which made for a confusing credit consumer!)
Typically, most people furnish information to the big three on a monthly basis.. so you will see a change in your score every-single-month.. .(unless you are a credit freak like I used to be and you check it everyday!)
any day of the week, any number of your creditors or collectors can (and will) "update" their tradeline in your credit file.... this will result in a (newly generated) different score.
If you are totally interested in your credit and all that good credit stuff... I would like to tell you to go over to
www.creditboards.com and READ READ READ
good luck!