This 19 page long short-story deals with the paradoxes of time-travel.
Read it, it won't take much of your time.
And oh, don't forget to read it again, immediately! It's more fun that way!
P.S. - Try not to think too much about the story if you happen to read it late in the night or you are bound to lose some sleep while you try and contemplate the paradoxes of time-travel.