The graphs below show percentage distribution of delivery time from Poland to other countries in period of last year (from September 2015 to September 2016). The unit is calendar day from shipment to delivery to end user. It include weekends and holidays, failed delivery attempts when user is not at home, just real life conditions. Data was taken from Polish Post tracking system, sometimes from other national posts if data are not complete.
This data should help you estimate delivery time and shows how it may vary.
For some countries like USA, Canada or Australia tracking system doesn't works, so I can't present data.