I cannot give you an average time – it depends how easy or difficult you find the topics.
Our lectures (together with our free lectures notes) are a complete free course for Paper PM and cover everything needed to be able to pass the exam well.
The only book you need to buy is a Revision Kit from one of the ACCA approved publishers (BPP or Kaplan) because they are full of past exam questions (and other exam standard questions) for practice – practice is vital to passing the exam.