Yep, that's correct when you buy that postage label it records the date and tracking for that day for dispatch of the item, holding onto the item for any length of time after dispatch time , think for SD it's 1 - 3 days, you will get a late delivery mark.
Cheeky of buyers to ask to post when they know they cannot accept delivery. Should you be asked again explain the sanctions applied when doing this, and that the item will be cancelled with their agreement this refunds them, and that it will be relisted at a time when they can buy it again from your eBay listing and be home for that delivery!
@garys6738