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.
With 29 in each leap year). The number of days in each month can also be found by counting across the knuckles and valleys on the back of each clenched fist (from left to right): Each knuckle month has 31 days, while each valley month has only 30 days (excepting of course February).