You have 60 days, why wait so long that you are out of time? You might as well leave fb when received, it does not stop you, should there be a reason, from returning, you can still open a case.
If you have gone over the 60 days from purchase, then it is too late to leave feedback.
You cannot delete purchases, but on Purchase History page, you can hide them. Go top left of the page, and click on Hidden. or right of each item, More Actions >> Hide order.
