unequally spaced time interval

[cvl]

Can unequally space time interval be specified by models such as AR, ARMA or TOEP?
or I need to use SP(Pow)? If so, could anyone show me how to do it.

Another more fundamental question , is it necessary to include time effects anytime conducting longitudinal or time series data if time is not the interest.

Thank you

[lvm]

If you collect data over time on the same experimental units, you need to account for the repeated measure in the statistical model, whether you care about time or not. If times are not equally spaced, you should normally use one of the of the "SP()()" structures in the repeated statement. You need a variable for time (let's call it time). Then, you could use
repeated / sub=subject type=sp(pow)(time);
where subject defines the experimental unit.

If the times are close to being equally spaced, it is probably a reasonable approximation to use ar(1), or one of the other ones.