Niagara Scratchpad how create increasing variable?

I’ve managed to make way on this. For the Timer, added the (Emitter)“Timer” variable with DeltaTime set within a Set Parameter within Emitter Update. Which works fine.

But now am stuck trying to increment my Index variable when a duration is reached. The biggest problem is knowing how to get the variable passed to MapSet, usually within a Blueprint I just use Get X + Y and Set.