Missing payments. If you don't see a recent payment you've made, make sure you've allowed enough time for the payment to post to your account: Payments made by electronic check, by credit card, at a T-Mobile store, or over the phone usually post to your account right away, but it can take up to three hours.
Nothing in-game uses Kerbin days/years as far as I can tell. A day is defined as 86400 seconds, and a year as 365 days.
there are 12 seconds in a year: January 2nd, February 2nd, March 2nd, April 2nd, May 2nd, June 2nd, July 2nd, August 2nd, September 2nd, October 2nd, November 2nd and December 2nd.