"Day and night" in the line "I keep a-wonderin' 'bout her day and night" is a merism.
In the line "I'm gonna search everywhere," the "every-" of "everywhere" is sung with three syllables, giving a sense of thoroughness.
As if to reflect the searching nature of "I looked around; I climbed up high into the dawn...," there's something of a key change. The verses are in C major, but this section is in a flat key.