If "at the same time" is meant to modify "the same goods", so that what you're saying is that discounting does not involve assigning different values to "good-g-at-time-t", then this is false. Depending on the time at which the valuation is made, discounting entails that different values will be assigned to "good-g-at-time-t".

Suppose an agend with exponential time discounting assigns goods G at a time T a utility of U0(G)*exp(a*(T0-T)). Then that is the utility the agent at any time assigns those goods at that time. You may be thinking that the agent at time TA assigns a utility to the goods G at the same time T of U0(G)*exp(a*(TA-T)) and thus the agent at different times is assigning different utilities, but these utility functions differ only by the constant (over states of the universe) factor exp(a*(TA-T0)), which being an affine transformation, doesn't matter. The discounting agent's equivalency class of utility functions representing its values really is constant over the agent's subjective time.