Haleigh got out of school at 3:00, I think it has been said that the bus dropped off between 3:30 and 3:45 - would of been plenty of time for RC to pick up Haleigh and make it to work by 4:30.
The reason Misty gave for Ron picking up HaLeigh alone from the bus stop on Monday was because Jr was taking a late afternoon nap. She stated this on the voice analysis test I believe.