Reports are based on an underlying data period of either aggregated parcel counts or 50-day transactional data where you can drill through. The data period used for each report is specified at the beginning of the article on it.
The manifest date selector, where available, reflects the associated report's underlying data period. It allows you to filter the data according to a particular range of dates on which shipments were manifested from the warehouse:
You can either use the slider to control the date range or click on the actual dates at either end of the slider and select the From and To dates via a date picker.