Onestream stores data as YTD, so if you calculate a later month, it will have to calculate prior periods to figure out what the YTD numbers at that point look like.
The scenario range is a Workflow-related property that determines which periods will allow for data input through the workflow. As far as I understand, behind the scenes, those periods don't disappear into thin air, they will just have no data (as long as you set the Number of No Input Periods Per WF Unit property).
In practice, this shouldn't be a problem - if you set the properties right, the previous periods will always be totally empty, so processing time should be basically irrelevant (assuming good rules are in place).
