Yes, get there before 9am because it's cool to see the park come alive in the morning. Walk up to the gate around 08:30am. Go into IOA, take a lap, and everything is a walkon. I know you'll have magic keys, but it's still good to get there early. Why? Because the park is less crowded, and the temperature is lower.
Around noon, the sun is over head, it's hot, and the tour busses have arrived. Park starts to get crowded and hectic. That's when you go back to your hotel room for lunch and a nap, then come back around 4pm. March won't be as bad in terms of the temperature, but in July/August, it's brutally hot in the afternoon.
I'm going March 30/31 and I'll be at the gate before they open each morning.