After activating Standard Procedure’s ability, it stays revealed in your hand until the ability resolves. If Standard Procedure is no longer in your hand at that time, it won’t become the chosen card.

The chosen card must be Standard-legal, even if you’re playing a different format.

Standard Procedure’s effect isn’t a copy effect. It becomes the chosen card until end of turn. Treat it just as though it were the chosen card. For example, say you chose Lightning Strike. That card is now Lightning Strike. After you cast it, it would go to your graveyard. If it got shuffled into your library, it would still be Lightning Strike. You could then find it while searching your library for a red card, for example. For all intents and purposes, it is the chosen card for the turn no matter what happens to it.

At the time of Unfinity’s release, the following card sets are permitted in the Standard format: Innistrad: Midnight Hunt, Innistrad: Crimson Vow, Kamigawa: Neon Dynasty, Streets of New Capenna, and Dominaria United. Notably, and thankfully, Unfinity is not Standard-legal. Go to Magic.Wizards.com/Formats for a complete list of formats and their permitted card sets and banned lists.

If you choose a card with in its mana cost, is considered to be 0 when determining whether the card’s mana value is 3 or less.