PDFs normally upload quite fast, being just text documents with few other features. While the final time will likely vary depending on your internet speed, your PDF file shouldn’t take much more than 5 to 7 minutes to upload into KDP. If it is taking longer or frequently freezes before being unable to continue, this could be a sign that there is an issue with your PDF, possibly due to formatting errors. When in doubt, it always seems to come back to formatting errors!