I called my banks about a year ago to ask. Capital One, Chase, and Barclays happily told me. Wells Fargo and Synchrony gave me unhelpful answers, but they didn't refuse to answer. I got my AMEX card later and never bothered asking because I knew what to expect from reading here.
Most cards report the statement balance on or soon after the statement date, and the Citi Best Buy card would be among them. An easier question to ask would be when your statement cuts if you're unable to figure that out. That's an important piece of information as with some cards, statement dates shift a little from month to month.
Exceptions to typical reporting include US Bank and Chase. US Bank reports one's balance as of the first of the month. Chase reports the statement balance like most cards, but they also report zero whenever you pay to zero. And additionally, they'll report whenever you ask them to.
Your best bets are to look at your reports or to ask here. 
We have that information about cards from the larger banks.
