how to define sampling time in the case of discretization of continuous time state-space model?

I have a two input-two output continuous time state space model and i need to discrete it. but i dont know how to define sampling time for discretizing.

A=[-.0052 0 .0083 0

0 -.0050 0 .0081

0 0 .0083 0

0 0 0 .0081];

B=[.006 0

0 .0030

0 .0014

.0012 0]

C=[1 0 0 0

0 1 0 0]