How two transactions with the same hash can cause double-spending
The scenario your tried to imagine is almost correct. 

The point is that the "attacker" will generate two identical transaction coming from the same unspent outputs of his address X to "Vendor" address Y. He will generate T1 and T2 at the same time, taking funds to send from the same source but he will attach to each transaction a different fee. Of course one of the two transactions will have an higher fee.

The transaction with the higher fee (i.e. the tx which the "attacker" sends back to his owned address, as you called T2) will be the one ACCEPTED by the network. T1 will be rejected because it comes from the same unspent outputs than T2 but it has a lower fee, so after a while it gets pruned by mempool of Bitcoin network.

In conclusion, pseudo double spending, it's a matter of fees and not tx timestamps. 

Hope this helped.