shadows of sun, time, sundial
晷 centers on measuring time through the sun's shadow: a sundial, the shadows it casts, and by extension time itself.
晷 combines 日 (sun) with 咎, which likely contributes the sound and relates to measuring or marking. The character expresses a sundial or the sun's shadow used to tell time.
The sun 日 sits above 咎, which looks like a person with a measuring tool. Picture a person using the sun's shadow to mark time on a sundial.
For キ, imagine a key-shaped shadow cast by the sundial: key -> キ, and the shadow tells the time.