Bottom line is you can't control the future. You might have already missed that window that gives you the smoothest airline career ever, or you are just making it in by taking this class but now your family resents your career forever, or you wait and take the vacation with a later class and have a great time but your career winds up with rough patches, or you take the later class and the vacation which opens up an opportunity you never had. I could go on forever with how this all plays out. Choose what you feel is best for you and your family.
I am heading back after a few years break from flying. My wife isn't happy about it, but I think my marriage would be worse off with me resenting my family as the reason I don't fly anymore. My wife isn't happy, but she agrees. Do what is best for your situation.