I worked 5 days in one work week, total of 12 hours per day for a total of 60 hours.
Is overtime for the week 20 hours, 4 per day? Or is it 32 hours (OT) because I reached 40 hours in the 4th day of the week?
Please advise, thanks.

Mon 12
Tues 12
Wed 12
Thur 12
Fri 12

The daily overtime is not counted towards the the 40 hours a week. Thus, the proper pay for your hypothetical is to pay 8 Straight Time and 4 Overtime for each of the 5 days. It is difficult to find an authoritatize source for this, and I am frequently asked this questions. As such, I have dug up an interpretation from the DLSE that agrees with me. The relevant quote is here:

Once an hour is counted as an overtime hour under some form of overtime, it cannot be counted as an hour worked for the purpose of another form of overtime. When an employee works ten hours in one day, the two daily overtime hours cannot also be counted as hours worked for the purpose of weekly overtime.


You can find complete analysis of the law that re-instated the 8 hour day here:
http://www.dir.ca.gov/dlse/AB60update.htm

The wage orders also explicitly state this principal for alternative work weeks.