dual degree programs are designed to save you time, as well as put more physician-scientists in the academic world. most programs are combined in the format of 1st two years of d-school (didactic/preclinic), then 3 years or however long it takes you for PhD (namely, thesis research), then last 2 years of d-school (clinic). some schools are different, for instance, ucla does 3 years of school, then halftime in clinic to finish 4th year reqs while starting PhD research.
good luck.