I am a very satisfied Disney College Program Alumna. I participated during the first semester of my Junior year. I would suggest working with your college counselor, who is familiar with your major, to discuss when the appropriate time would be to take a break from your studies. While educational opportunities do exist (and are required for a DisneyLand CP), not all universities will give you credit for taking these classes.
For most, the sooner you participate, the better. The Disney corporation can teach you so much, connect you with fascinating professionals, and expose you to a world of opportunities!
P.S.- when it comes time to interview, remember to SMILE! Even if you are over the phone, they can hear it!
You can apply as a freshman for your second year to be in the program and definitely should apply as soon as you can
I would encourage you to apply as soon as you can so that if you do not get in the first time you will be a second time applicant the next time and more likely to get in. It shows that you are committed to participating by the fact you did not give up if not accepted the first time and gives you the most opportunities to get into the program
Depending upon your area of discipline and how many college credits you currently have (meaning at what point in college you are at currently), it is best to seek information out from your College Academic Advisor first. If possible, try to plan for your internship at Disney to be between your breadth coursework and your major coursework. Typically, this would be after completion of your sophomore year. If you can plan it during the summer, it would be ideal.