When Inspiring Captain enters the battlefield, creatures you control get +1/+1 until end of turn.
Inspiring Captain’s triggered ability affects only creatures you control at the time it resolves. Creatures you begin to control later in the turn won’t get +1/+1.
The set of creatures affected by Inspiring Captain’s ability is determined as the ability resolves. Creatures you begin to control later in the turn won’t get +1/+1.