A sample and hold circuit is implemented using a resistive switch and a capacitor with a time constant of $1 \; \mu \mathrm{s}$. The time for the sampling switch to stay closed to charge a capacitor adequately to a full scale voltage of $1 \mathrm{~V}$ with $12$-bit accuracy is ___________ $\mu \mathrm{s}$ (rounded off to two decimal places).