A time or the time What is the difference between Do you have a time and Do you have the time?

Do you have the time? -means what time is it?

Actually it means: Do you have a watch to tell the time and if you do than tell me the time, please (not just the fact that you do!)

Also Do you have the time, could also mean have you any spare time to help someone or do something...and Do you have a time, could mean an appointment