We can capture the number of days the opportunity stayed in a stage using custom field+wf+field update. This works on the current records and on the existing records if they are edited(the value will not be equal to Standard Stage Duration field available on the Report).
Is there a way to capture the Opportunity Stage Duration Days on the existing records,making the resultant value equals to the Standard Stage Duration.
Edit - updated report name, and details below
There is a standard report type for opportunity history (distinct from opportunity field history).
This report does not include stage duration, but does track the date of each stage change so you could calculate the duration.
You could run this report, export the value, and load via data loader.
Can't find good documentation on this yet. Will keep looking and will update the post when I do, but if you search your report types it should be there.
