355.5. If a card requires you to specifically choose one or more Game Objects, that choice is made now.
355.5.a. This does not include cards that affect one or more Game Objects based on criteria. Example: "Stun a unit at a battlefield" is a Choice. Example: "Kill all gear" is not a Choice.
355.5.b. This does not include making choices for Triggered Abilities of permanents, even if those abilities trigger when the permanent is played. Example: A unit with a triggered ability that says "When I'm played, kill a unit" does not require you to choose a target as it's played. The target will be chosen when the ability triggers. See rule 382. Triggered Abilities for more information.