The capacitance time constant characterizes the physical quantity of the response change speed during the transient process of the circuit. Has a time dimension. The smaller the time constant of the circuit, the faster the response changes, and the slower.
The time constant is the product of resistance and capacitance CR. If the unit of C is μF (microfarad), the unit of R is MΩ (megaohm), and the unit of time constant T is s (seconds).