I think that an effect of the time structure of the story is to reveal the destabilizing condition that racism has on its victims.  Baldwin shows that White society is just as much a victim of racism as people of color.  Naturally, there is much more perpetrated by White society upon people of color, but it is in this where they,too, are victimized.  

Racism is shown through Jesse and his night trying to sleep and trying to have sex.  His impotence is a part of the condition of racism of which he, himself, is a part.  Racism is shown to be such a destructive force in that when Jesse is unable to sustain an erection, he has to reflect about his own life.  This reflection is where one sees how racism has impacted his being in the world.  The conditions of  violence, segregation, hatred, and force are all remnants of Jesse perpetrating the condition of racism.  His reverie and reflection into this world is one in which racism has prevented him from being able to fully understand and coherently articulate his condition.  The reader understands this as the narrative shifts continually, with racism being the underlying force.

Baldwin is able to construct Jesse to be one who is literally inhibited by the condition of racism that prevents him from being an effective human being.  His impotence is only resolved when he himself becomes that which he detests.  When Jesse tells his wife that he "is going to do her" as a man of color, it is the culmination of how Jesse's own notion of self has been distorted because of racism.  This distortion is complete in that his reveries move from time to time, place to place and in no coherent order other than the social condition of racism is the constant.  It is for this reason that the narrative's structure is challenging to the reader.  Racism is challenging to the reader and seeing the effect it has on Jesse reminds the reader that there is a distortion intrinsic to a social order predicated upon discrimination, making its perpetrators victims in its own right.  This distortion in time and narrative space is where the reader understands this in Baldwin's work.