What is the best way to get the time off from work for a second interview?

Today, I took the day off from work (which is next to impossible because my boss doesn't give time off) I had an interview for another job. Now, they are wanting me to come back for a second interview next week. My work does not give vacation, sick, or personal days. What kind of excuse can I give to leave early for an interview. My excuse today was my doctor wants to run some tests on me and they have to do some blood work and my father is taking me because usually it makes me ill afterwards so I wouldn't be back for work after the appointment.