There are, apparently, two variations on the same dream in this poem. In the first, the speaker dreams that he might:
. . . fling [his] arms wide
In some place of the sun,
To whirl and to dance
Till the white day is done.
There is something that seems restrictive about the day: first, he associates it with "white[ness]," and second, he can only dream of whirling and dancing during the daytime—implying that it is something not typically allowed him (perhaps because of his race). The idea of whirling and dancing seems to have power, because it is something he aspires to and dreams of doing; to do it would be fulfilling and empowering.
In the second variation on the dream, the speaker longs:
To fling [his] arms wide
In the face of the sun,
Dance! Whirl! Whirl!
Till the quick day is done.
Now, the day is "quick" rather than "white," and so perhaps this dream variation is a more advanced version of the first one. "White[ness]" is no longer privileged—unlike in the first variation, the night is "Black like me." Dancing and whirling seems like something equalizing, as though being able or allowed to dance and whirl would help to promote and maintain racial equality.