An elementary liquid phase reversible reaction $P \leftrightarrows Q$ is carried out in an ideal continuous stirred tank reactor (CSTR) operated at steady state. The rate of consumption of $P, -r_p$ (in $mol \: \text{litre}^{-1} \text{minute}^{-1}$), is given by $$-r_P=C_P-0.5C_Q$$ where $C_P$ and $C_Q$ are the concentrations (in $\text{mol } \text{litre}^{-1}$) of $P$ and $Q$ respectively.

The feed contains only the reactant $P$ at a concentration of $1 \text{ mol litre}^{-1}$, and the conversion of $P$ at that exit of the CSTR is $75\%$ of the equilibrium conversion. Assume that there is no volume change associated with the reaction, and the temperature of the reaction mixture is constant throughout the operation. The space time (in minutes) of the CSTR is ______ (round off to $1$ decimal place).