$\lambda=\frac{ V }{\sqrt{2} \pi d ^{2} N }$

$V =$ Volume of container

where: $N =$ No of molecules

Hence with increasing temp since volume of container does not change (closed container), so mean free path is unchanged.

Average collision time

$=\frac{\text { mean free path }}{V_{ av }}=\frac{\lambda}{(\text { avg speed of molecules })}$

$\because$ avg speed $\alpha \sqrt{ T }$

$\therefore$ Avg coll. time $\alpha \frac{1}{\sqrt{ T }}$

Hence with increase in temperature the average collision time decreases.