New to InstantCert - Need Your Opinions on Prep & Study Time

[Duncoboy]

I've just signed up for InstantCert - I have approx. 15 exams (combination of DSSTs and CLEPs) standing between me and my degree. I work full-time, and I'm wondering if any of you out there can give me advice on generally how much time should be given to prepare for each exam using InstantCert? I'm planning on taking the following exams:

DSSTS:
Foundations of Education
Civil War & Reconstruction
Developmental Psychology
Contemporary Western Europe
A History of the Vietnam War
Organizational Behavior
Rise and Fall of the Soviet Union
Human Resources Management
Substance Abuse: Fundamental Facts
Ethics in America
Physical Geology
Environmental Sci: The Race to Save the Planet

CLEPs:
American Government
Intro to Educational Psychology
Natural Sciences I

Please let me know if you've taken any of the above exams, and if so, how much time you'd taken to prepare with InstantCert in order to get a passing grade.
Thanks!