Low-complexity generation of single pulse using RC circuit from a fixed DC supply without the use of a controller
simulate this circuit &ndash; Schematic created using CircuitLab

Figure 1. A faster discharge can be obtained with D1.

The true answer depends on what the load is. If, for example, your circuit draws 1 mA then the capacitor will discharge at a rate given by \$ \frac {dV}{dt}= \frac I C = \frac {1m}{470\mu} = 2 \ \text {V/s} \$. 

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