starting lemonade diet friday never fasted before

Hi everyone, a friend of mine told me about this lemonade fast a couple of months ago and I have been researching and waiting for the right time to start. I just stumbled on this website today and I think this is great!! I am excited and scared and hope to be feeling great on this fast. I am going to start on Friday and I want to do 20 days but my question is I have to travel from TX to California on Sept. 13th and I will spend like 7 hours on a plane and have to take a client to lunch so I could only do like 14 days and then break the fast in time to be able to eat on the 13th! Could I go right back on the fast after that day for another week or so? Or would that be to upsetting for my system?
My goal is to break my bad eating habits. I plan to go to a mostly vegetarian diet after the fast. I want to quit all dairy, Sugar and meat except fish and egg whites. Any and all advice would be greatly appreciated. I am truly a virgin when it comes to this kind of thing!!

Susan