How USCIS counts full time CPT days

I know that full time CPT should not be more than 364 days in order to maintain OPT eligibility, but I don’t know how the days are counted.

As most of you know that I am a premed with Chem.E major, I HAVE to do Co-op for my career prospect, and I know it is at least 3 semester: summer, fall, and spring. That would mean I have to apply for full time CPT if I am hired for Co-op, and I want to keep it less than 364 days because I also want to do some kind of internships for medical schools. I don’t want to lose OPT eligibility.

The problem is, how do USCIS count those full time CPT days?

For example, let’s say my Co-op is 3 semesters long, requires me to work for 30 hours per week, 6 hours per day. That would be 5 days per week. Do they only count the day I actually work? Or do they count days that I am enrolled in Co-OP? Do they also count holidays that I am not working?

Yes. “Total time used: All days in CPT period. Includes weekends, holidays, vacation days, and even
time outside the U.S. during CPT”

Well that is totally disappointing…hope I can get internship in our school medical cneter