The time constant for the discharge of a capacitor in a RC circuit is given by
[tex]\tau = RC[/tex]
where R is the equivalent resistance of the circuit and C is the capacitance of the capacitor. The time constant corresponds to the time after which the charge on the capacitor has reduced to [tex]e^{-1} \sim 36\%[/tex] of the initial charge on the capacitor.
Since it is a time, the units of the time constant are seconds:
[tex][\tau]=[s][/tex]
