stretching ns analog pulses for digital conversion
You are trying to charge a 330 pF capacitor up very quickly. Going by information from your other question this needs to be done in about 1ns. Given your pulse maybe be (say) 1V in amplitude you can work out how much current the op-amp has to supply to charge the capacitor up....

Q=CV or... 

dQ/dt = C dV/dt (note that rate of change of charge equals current)

So current = 330pF * 1V per nanosecond = 330 mA

You are not going to find a fast enough op-amp that can supply this amount of current with any degree of accuracy.

You are going to be looking at something around 10pF rather than > 100 pF and you are going to need a much better op-amp as has been mentioned in the other answer.