I've had my AmEx Delta SkyMiles card since October/November last year, and it finally occurred to me to call them and see if I can get an increase (purely for FICO-improving purposes) on the initial $2800 limit. They instantly agreed to up my limit to $7400, which was nice. 
So... can anyone tell me how long it might take them to report the new limit to the CRBs? Hopefully they'll do it in a more timely fashion than their balance reporting - why DO they have to report the balance from the previous month's statement, and thus always be two months behind, huh? I'm hoping that the new credit limit will have at least a small (good) effect on my credit scores - I have 5 cards in total (Capital One - $750 limit/$0 balance, US Bank - $500 limit/$0 balance, Banana Republic - $500 limit/$0 balance, Macy's - $700 limit/$0 balance, and the AmEx card - previously $2800 limit, now $7400 limit, and a $400 balance) and this is the only one with an even halfway decent credit limit on it, so the CLI should make a noticeable difference. I hope.
So... can anyone tell me how long it might take them to report the new limit to the CRBs? Hopefully they'll do it in a more timely fashion than their balance reporting - why DO they have to report the balance from the previous month's statement, and thus always be two months behind, huh? I'm hoping that the new credit limit will have at least a small (good) effect on my credit scores - I have 5 cards in total (Capital One - $750 limit/$0 balance, US Bank - $500 limit/$0 balance, Banana Republic - $500 limit/$0 balance, Macy's - $700 limit/$0 balance, and the AmEx card - previously $2800 limit, now $7400 limit, and a $400 balance) and this is the only one with an even halfway decent credit limit on it, so the CLI should make a noticeable difference. I hope.
Everytime I've gotten a CLI it reports at the end of my billing cycle, along with whatever my new balance is. I don't know if this is always the case, but it has been my experience. 
@FretlessMayhem wrote:
I've noticed AMEX typically updates at the end of the month, using the previous statement's balance and CL.
I've seen others concur, and this is definitely what happened for me.
BOA however, sends out special updates on CLs.
That's definitely what they do for me, too - they report the closing balance of the previous month's statement. If they report credit line increases at the end of the billing cycle too, I've got a few weeks until my new limit appears on my credit reports. Will be interested to see whether I get some score improvement from it!
Thanks for the quick responses!