Allright, I guess I’m going to be that guy….
I’m surprised no one has said this, but if you are shipping slabs and using paper towels for packing material, you are asking for trouble. Doesn’t matter if you’ve done it before and it turned out okay. Eventually you’ll wind up with a cracked slab and an irate buyer, possibly a neg and be out the cost of the slab and shipping when ebay finds in the buyer’s favor.
Always, always, always use a ton of bubble wrap or bubble wrap with packing peanuts. Paper towels are not going to absorb and stand up to any impact if the box is damaged. For a valuable book I’d suggest double boxing. These packages aren’t getting some white glove treatment – they’re getting tossed into trucks, across rooms into bins and through various mechanical sorting machinery. Pack a slab as if you expect the box to be handled by a gorilla; pack a slab the way YOU would want to receive it.
Secondly, why aren’t you generating postage and printing it through ebay? You don’t have to remember to enter the tracking number, it’s automatically attached to the listing. It’d the easiest and fastest way to ship.
Finally, go to your seller dashboard and change your handling time. What's to figure? If you can't find it in your menu items, ask Google how to change it. Again, you’re just setting yourself up for problems.