Does anybody know if a person's circadian rhythms can be changed and how long it takes to do it?

I am retired now, but all my working years I tried to change my circadian rhythm because despite the fact that I would come home from work exhausted at 6 p.m., when 9 p.m. came around I would "perk up" and get the energy that I lacked all day long..... I would go to bed @ 1:30 or 2:00 and had to get up at 6:30. "Day" people would try to tell me that it was just "habit".......but no matter how much sleep I got, I was never 100% ffunctioning during daylight hours. I still joke with friend who go to bed at 10:30 or 11:00 and "can't understand how I can sleep so late in the morning" (I'm retired....why do I still need to get up with the birds???) and I tell them that when they are crawling into bed I am just getting into second gear. Over the years I have tried to change this, but my ENERGY is still only at night. Now that I am retired I just "go with the flow", but when I do have to get up (what I call) "early" (before 10 or 11 a.m.) I am still dragging all day.....so now when I have to make an appointment (hair, doctor, etc.) I always make it for mid or late afternoon. Still....you will never be able to convince the people who bound out of bed at 6 a.m. ready to start their day....that there are different body rhythms that you may be able to work around, but never change.