It concerns time spent in the relevant classification, and the counting depends on the individual's own history, including earlier assignments and any change between classifications. The general figures are a starting point only; exceptions, and how they apply to a particular record, require assessment by a licensed United States immigration lawyer.
Bring the history, not the conclusion
An employee who arrives with a fully worked-out theory of how much time remains often has to unwind it. The more productive approach is to bring the underlying records and let counsel do the counting. Where an employee has held more than one classification, or worked in the United States for a different employer years earlier, say so explicitly, because those periods can matter to the analysis.
It helps to know which facts an employee most often gets wrong when reasoning about this alone. Time held in a different classification, a short period working in the United States for another employer years earlier, and periods spent abroad that were assumed to reset something are the three that recur. Each of them can matter, and none of them is safely assessed from a general description of the rules.
Bring the approval notices, the admission records and the passports covering the whole period, including expired ones, and let the counting be done from documents. An employee arriving with a conclusion generally has to unwind it before any useful advice can begin.