Without the Book of Job giving any definitive time markers or specified number of days or years, we cannot know how long Job suffered.  We can know that it had to be more than a just a few weeks based on:

• one day of calamity in Job 1
• an apparent gap between Job 1 and 2
• the time it took for the three friends to hear about Job and travel to visit him,
• one week of the friends sitting in silence with Job
• the three friends speaking,
• the fourth friend speaking, 
• Job speaking, 
• God speaking,
• God commanding the friends to offer sacrifice
• the friends’ departure
• Job praying

It was only after Job’s three friends left (Job 42:9), and when Job prayed for his friends, that God restored Job (Job 42:10).  

Some have suggested the course of events might have been as long as two years, which would mean Job suffered for that time.  Others have suggested it might have been 42 months, as a whisper of the Great Tribulation.  But again, there is no way to determine how long Job suffered. The Bible simply does not say.  This might be why the book of Job is not included with the historical books, but instead is part of the writings. Without any specific mention of dates or historical events it is impossible to conclusively date the book or determine the length of events and Job’s suffering.