Period setting changes the data displayed in all the views of HP Designjet Partner Link Pay-Per-Use portal. The period setting is based on collection date: 

Collection date: is the time registered when the job is collected from PPU web portal. The "Last Collect" will update only when a new job is received in Partner Link. Note : It could happen total usage can be received before the job
Print timestamp: is the time registered by the device when the file is finished to print. This is the printing time in the printer accounting (EWS)

Please notice that the period setting of a report has to be set inside the report configuration.