how to reduce turn-off delay time of PNP transistor
Your circuit is slow because of the way you are using the optoisolator.

Because of the gain of the transistor, the effective load at turn-off is more than 1M\$\Omega\$, so you can extrapolate the curves to see what kind of trouble that causes.
So reduce the load resistance to something like 1K and your error will be greatly reduced.
Here is your circuit, changed about as little as makes sense, which behaves much better:

I've increased the optoisolator LED drive current (to about 4x the load current to account for the minimum 50% CTR, aging and temperature), and increased the load current to speed up the response.