dawn, early morning, day
昕 centers on the first light of day: dawn, early morning, and by extension the day itself as it begins.
昕 combines 日 (sun) with 斤, which likely contributes the sound. The exact historical role of 斤 is uncertain, but the character is understood as representing the rising sun at dawn.
The sun 日 rises beside an axe 斤 at dawn, as if chopping through the darkness to start the day.
For キン, imagine the sun's first light glinting off the axe blade: glint -> キン, and the dawn breaks.