You can apply for the 3+3 program while you are in high school at the same time you are applying to Temple University and the College of Public Health. Make sure you choose the B.S. in Health Professions as your major because it is the only major in CPH associated with the program.
The office of Pre-Professional Health Studies has information about applying on their website.
If you are still interested in the 3+3 program, or didn't know about it, you can still apply for the program in your first semester of your freshman year for admission. If you are not in the B.S. in Health Professions you will be required to change your major once admitted to the 3+3 program.
The office of Pre-Professional Health Studies has information about applying on their website.