Spoiler Alert:

Cooper was unable to go back in time, or into the future. When he slipped into the singularity he entered a 4 dimensional place constructed in a 5th dimensional reality by human beings of the future. He had access to the timeline of what he had already experienced but he could not materialize in the past, or in the future. In the 5th dimension, gravity/time becomes like one of our 3 dimensions here. The dimensions we interact with physically include length, width, depth, and height. In the 5th dimension time/gravity becomes a physical dimension, thus Cooper is able to program the quantum data into the watch by affecting one of the watch hands with gravity from the 5th dimension. When he is done, he is spit out at the present which is many years into the future because of time dilation, but he did not choose where to go in time and could not, he could only interact with the timeline of what he had lived up to the present.