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.
How Many Days Calculator-count days in a year. This site provides a tool to count the number of any selected day of the week over an entire year. You can pick any year and find out things like the number of Tuesdays in 2015.1. Today is Wednesday, October 14th, 2015. It is the 287th day of the year, and in the 42nd week of the year (assuming each week starts on a Sunday). There are 31 days in this month. 2015 is not a leap year, so there are 365 days in this year.