It depends on several different factors, but normally you can walk on it CAREFULLY (No twisting!) in about 12 hours. After 48 hours you can remove the forms, but it’s better to leave them on for a whole week if possible. In 2 weeks you can park a car on your concrete. After 28 days, the concrete reaches its full strength.
Air entrapment means the induction of very small air bubbles into fresh concrete. When the concrete hardens, the air bubbles form small voids, and these voids give concrete additional durability in freezing or thawing conditions.