system identification(Using demo(ident))

1- I learnt to identify systems like:

               k1
y= ------------------------- * x
        (1+T1*s)(1+T2*s)

I used "Process Model" in "ident" GUI and every thing was OK. but what can I do if the sampling intervals were not same?

I forgot to say I'm using MATLAB r2011a and i have access to Matlab 2012a at university

sorry for my bad English Best Regards Amir