If I recall, Citi's 24 mo for TY and 48 for AA is from the point when a card is open/closed, not when the bonus was earned. Standard practice had been to keep cards open for more frequent apps, while reducing their respective CLs to increase odds of auto-approval--this was assuming one's Fico score could withstand such tinkering. At least in my experience, Citi had no qualms with anyone having a gazillion of the same card.