operator keyword usage in c++

Question

I know the operator keyword can be used to overload operators such as +=, -= or even the function call operator ().

I came across this code and cannot understand the syntax of lines A and B.

What do these two lines do? If they declare functions, how should the functions be used?

using INT64 = long long;
class Time
{
public:
    INT64 microseconds;                               // data member
    Time() : microseconds(0) { }                      // default constructor
    Time& operator+= (const INT64 msec);              // overloads += operator
    operator INT64 () const { return microseconds; }; // line A ???
    operator const timespec() const;                  // line B ???
}