depends when you submit your readings. For example, If you submit them 2 days before your payment date, PP will estimate the usage for the last 3 days, but use your readings for the rest of the month.
When PP request my readings , I don't send my readings until the last day possible. Ie PP say they need them by 1st, I send mine 31st. And mine are not being estimated.
However, when you submit your next ones, previous ones will be adjusted. Hope this helps.