A standin can load an animation sequence, such as circling_cubes.[1..25].ass.
For example, if you open an Arnold_Standin property, click Browse, and select a sequence, Softimage automatically inserts a [Frame] token into the file name:

By default, that [Frame] token resolved to the current frame, but you can override that and use an expression to drive the sequence.

For example, if you have a 25-frame sequence of ASS files, you may want to play the 25 frames and then stop. To do that, you could use this expression:

 
MIN(Fc,25)
 

If you wanted to continuously loop the 25 frame sequence, you could use an fmod (modulo) expression like this:

 
cond( fmod( Fc, 25 ) == 0, 25, fmod(Fc,25) )
 

And if you wanted to show just frames 10 to 25, you could use this expression:

 
cond( Fc<10 , 10 , MIN(Fc,25) )
 

If you’re not sure about these expressions, try playing with them in the Expression Editor. As you move through the timeline, watch the Current Value update in the Expression Editor.