Where can buyer leave a review if the order was autocomplete in 3 days?
No problem, If buyer want then he can give it 1 year later.
Are you sure about it?
This is incorrect. Buyers have 30 days after a gig is completed in which to leave a review. They can do this from the order page.
Check the Terms of Service at the bottom of the Fiverr main page for the rules as to how Fiverr works.