Just to add to what Jane has written & you've asked

You really shouldn't wait the whole 20 days after opening a dispute before escalating to a claim-at most I'd only give a seller 24 hrs if you've never dealt with them before & they're ignoring you or trying to fob you off.Paypal also works on US time so at the very latest,I'd escalate to a claim on day 18.

Once escalated to a claim,the seller has 10 days in which to provide Paypal with a valid tracking number IF its an item not received claim.If its an item not as described,Paypal will give you the address to post it back to using trackable post which you MUST do within the 10 days & email & fax through a copy of the proof of posting back via a trackable method ie reistered or click n send.