Here is another way to look at it. What did you agree to when you were hired? If you agreed to work for a year then do what you promised. Explain honestly to your employment offer folks and tell them the truth. If they are worth going to work for, they will understand and offer you a later class date. If they penalize you for your honesty they aren't worth working for anyway. At times, a man's character is all he has. Do the right thing!