The item is paid on the date you lose control of the money. It's that simple.
When you write a check, the day you drop that check in the mailbox you have effectively lost control of that money. The item is paid as of that date. Doesn't matter if you write the check on Dec 31st. If the date on that check is Dec 31st and you mail it on Jan 2nd, you effectively "lost control" of that money on Dec 31st. Doesn't matter if it two more months before the recipient actually cashes the check.
