Do Temporary units count for Gutter Palace at the same timing, and can you react to Temporary?

Temporary and Gutter Palace share the same timing, so it is too late to react for Gutter Palace once Temporary is already on the chain. You cannot reveal or respond to Temporary at that trigger during the beginning phase. On the upside, your opponent also cannot react with Gust or similar to deny Temporary once it is on the chain. If you had 4 Temporary units at a battlefield that would satisfy Gutter Palace, they do count for the win condition when it triggers.