The seller cannot make up some date, the date for approximate delivery is on the listing. It is approximate not a definite date so worth waiting a couple of days past that date and then proceed this way:
Go right of the item purchased, and from More Actions select.... I Have Not Received My Item.
If you are not fully refunded within 3 days, you must escalate the case on day 4 or within 30 days from opening the case, and eBay will step in and force the refund.
Do not close the case early for any excuse or promise the seller may give, and do not forget to escalate.
@nielkothari