Pivot Table Regeneration Question

I'm finding some of the reporting needs I have in my application are best served via a Pivot Table report since selection of custom, on-the-fly date range in not easy to implement as it should be. Furthermore most of their access will more then likely be viewed by users on a smartphone to view their projected income for the week over a cup of coffee in the diner.

From what I can gather, there is no means to regenerate a Pivot report (following recent new data changes) from a smartphone. I'm asking how are "regenerations" triggered? Manually only, upon request? If they are "automatic" on the backend, how often can one expect this to occur?

I can't expect users to think to regenerate a number of pivot reports following data entry on a desktop. I really don't understand why these reports aren't generated on the fly upon request then served to the user.