When you install the Inventory Forecast Hero (IFH) app,
It grabs all the products from your store first.
Then app fetches the sales history from past 60 days, to update the orders of the products.
Typically it takes 1 minute to grab the 1000 products.
Also updating the 1000 orders takes around 1 minute.
Thus, the forecast page results depends upon the number of products available at your store.