pre-dawn
晗 centers on the moment just before sunrise: the pre-dawn twilight when light begins to appear but the sun is not yet visible.
晗 combines 日 (sun) with 含, which likely contributes the sound and the idea of containing or holding in. The character suggests the sun still contained below the horizon, i.e., pre-dawn.
The sun 日 is still contained 含 below the horizon. Picture the sky brightening but the sun itself not yet visible: that is the pre-dawn moment.
For カン, imagine a can of light waiting to be opened at dawn: can -> カン, and the sun is still contained inside.
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