the orbital period of Kerbin is listed as 1y 0d 0h 32m 24.618s (in the tracking center). Since Engineer lists time values by Kerbin years/days/etc, this should instead read 1 year exactly. The KSP wiki for Kerbin lists its year length as 426 d 0 h 32 m 24.6 s. Engineer must have been coded to consider one Kerbin year to be exactly 426 days long, which is inaccurate by 32 m 24.6 s. This means that any time value larger than 1 year will also be inaccurate, which will throw off precise calculations and planned orbits.