TCarson; I would seriously consider calling Citi about the issue of the time you had their system pull the money (it's stated on that site when it will be credited to your account also) and when they actually applied it. Explain to them you're concerned about the interest during those few days and are wondering if they system "self corrects" to post the payment as you requested through them. I've run into this before with other cards and called and had no problem. I've never run into this with Citi even though they're not my favorite CC LOL.
It does say if they receive your request before 5 p.m. EST they will credit your account that day, if after 5 p.m. they will credit the next day. There is a terms and conditions link in that notice you might want to review as well (I did not read that far into it, nor do I think it would affect your payment as you described).
These banks have to make $$$ if you are moving funds around. I don't see anything illegal about it. But yes.....100s of thousands of customers doing this and it's alot of $$$, but it's a drop in the bucket for them. If they don't make $$$ than they really can't extend credit to you and me and everybody else 
I pay both from my banks pay system as well as online with Citi. Citi is by far the fastest way to make the payment. If I pay through my bank, they take the funds 48 hrs prior to the date I designate to pay. They consider it processing time. If you want it applied same day, you should just use the Citi website to pay. I think you are limited to only 4 payments a month...someone will surely chime in if that is inaccurate.
Starting Score: TU:676;EQ:648 8/2011
Details from a Citi online payment through them:
@RyVision wrote:Details from a Citi online payment through them:
I work for BOA and when we say "credit your payment for the same day" it means, we count that you made your payment on that date, but the funds may not post to your account until 24-48 hrs later for your use and it may take even longer for the money to be taken from your account. So most likely you are getting credit for paying on let's say Monday, you can use the funds on Tuesday or Wednesday (depending on their cut off time), but the deduction from your bank may not happen until Wednesday or Thursday, which is just when they present the "check" to your bank for payment.
I just checked my Citi CC and Wf checking account. I have Citi set up to auto-pay on the due date. They both show the payment on the same day, the due day. Also, when checking my available credit it aways reflects the change as that same date.
It was that way when it was secured and remains that way now that the card is unsecured.
I actually would have preferred autopay to pay a few days earlier just in case something goes wrong so I don't get a late.
I'm surprised by all the negative experiences with bank bill-payment systems that have been reported since my earlier post in this thread. I've never experienced, and wouldn't tolerate, delays like that.
I've been using Bank of America's bill-pay system for over ten years, and in my experince they nearly always deliver my payments on the day they say they will. I keep a rolling six-month history of when each recipient actually credits my account, as shown on a subsequent statement. These are almost universally the dates I requested, with the single exception of my municipal water utility, which is routinely credited a day late.
I also track the delay until the payment appears on the payee's website, giving me a short-term confirmation that it was credited. This varies a bit more, from zero to three days. Variation among credit-card companies is typical of other creditors. Payments to Capital One always appear on their website on the date received. Bank of America's and USAA's websites sometimes show the payment on the date received, sometimes a day later. And American Express rarely appears until the day after receipt. But again, these are just when the websites first show the payment. What counts are when it's actually credited to my account, and that almost always happens exactly when I request it.
Yes, of course there's a processing delay. I do have to plan ahead a little, and schedule the payment two to five days before I want it to occur. But the payment isn't debited from my BoA account until they day I requested it be credited to my account at the payee.