I don't think you can do that for Auctions. If the Auctions have no bids you can close them, though. They will go to your Unsold List and can be relisted from there when you return.
For Fixed Price Listings, Go here- https://www.ebay.ca/vac/timeaway.
Personally I think it is a Bad Idea to leave your listings visible when you are not going to be able to ship promptly. Either you have an annoyed browser or you have an angry buyer who doesn't understand why you are not shipping.
Because; Buyers Don't Read ™
