why, of course my band of plucky heroes with two arms and two legs is travelling during a particularily nice spring through a faux-medieval countryside, and just before the sunset on a market day they arrive at a picturesque village that holds a terrible secret

The second [...] is defined by taking the fixed numerical value of the caesium frequency, ΔνCs, the unperturbed ground-state hyperfine transition frequency of the caesium 133 atom, to be 9192631770 when expressed in the unit Hz, which is equal to s−1. obviously, the world I am making has 60-second long minutes, 60-minute long hours, 24 hours a day; even though my world's OBVIOUSLY SINGLE sun makes apparent rotation around it in, say, 16 hours (Neptune), or 1500 hours (Mercury); sure I have 4 seasons repeating the same time of the "year", even though my world's orbit around it's sun (certainly that's the only place a story can occur on? no moons allowed!) has no axial parallelism; obviously inhabitants of my world can totally SEE that sun, no way it's obscured at all times by, say, just clouds (Venus), or the F*CKING ICE COVER, because we're living in a yellow submarine in a subterranean ocean (Enceladus); describe history in terms of 4-years long "olympiads", because WTF not; yep, weekends