“Twice” meant twice in a row.
No, twice means twice, regardless of when the two terms are served.
The only exception to the two term rule is if someone takes over mid-term for another President with less than half of the term left. In that case the person is still eligible for two full terms, but nowhere does it say that the terms must be served consecutively.
If someone took over another President's term with more than half of the term left, then they are only eligible to serve one more term.
So the maximum one person could potentially serve as president is 10 years minus one day, and the minimum they could be allowed to serve is 6 years plus one day.