GATE EC 2018 Set 1 Q2 — Electronic Devices

In the circuit shown below, the op-amp is ideal and Zener voltage of the diode is $2.5\: volts$. At the input, unit step voltage is applied, i.e. $v_{IN}\left ( t \right ) = u\left ( t \right )\:volts$. Also, at $t = 0$, the voltage across each of the capacitors is zero.

The time $t$, in milliseconds, at which the output voltage $v_{OUT}$ crosses $-10\: V$ is