XLPE cable Impedance from frequency to time domain - IFFT

Hello,

I have also 300 points vector impedance values in the frequency domain. It's part (z11) of frequency dependent (dimension6,6,300)) matrix of high-voltage three-phase XLPE underground cable in range from 10 Hz to 1 MHz. Each phase cable has own sheath and consequently impedance matrix has 6x6 dimension.
My objective is convert this impedance vector in time domain but - time simulation is determined: t=0.003 sec.
Therefore I used frequency step deltaf=1/3*1e+04 Hz (f: 10: 1/3*1e+04 : 1e+06 Hz) in determination of Z(omega).
In attachment you can find Zcca.mat (MATLAB mat file and simple Zcca.txt with impedance vector I must convert into a time domain.

My questions are:
1. How I can convert this impedance vector into 0:0.003 sec time period?
2. Have I choose correct frequency step (1/3*1e+04 Hz) in Z(omega) calculation? If it's not correct, which one I have to use?

MATLAB ifft code in .m file ar simple listing in answer would be highly appreciated!

Thanks in advance