0-conf transactions have timestamps and the receiving wallet/node checks for the tree of transactions to even allow the spending of unconfirmed transactions up to a limit of 25 for now, there is on-going research and testing to up this limit to 500 that was sponsored by SatoshiDice https://twitter.com/PeterRizun/status/1181980303033692162

For a list of transactions trying to double spend BCH and failing at it, see this https://doublespend.cash/