EBay gives you 60 days to leave feedback.
EBay allows you to Dispute Items Not Recieved (and Items Not As Described) for 30 days after delivery or last estimated day for delivery.
Don't worry about feedback.
EBay leaves your purchased items in your Purchased list for 60 days, after which you basically can't leave feedback nor open a Dispute.
So,
Mark that last estimated day for delivery on your calendar.
If the item hasn't arrived by then, go to the Resolution Centre at the bottom of this page and open an Dispute.
If you have items that you want to Dispute (for non-arrival usually) and the eBay deadline has passed, go to your Paypal account.
Their Resolution Centre is at the top of your account page under Tools.
You have 180 days from payment to Dispute through PP.
And your purchases stay in your PP account indefinitely.