boost::posix_time::operator>>
// In header: <boost/date_time/posix_time/posix_time_legacy_io.hpp> template<typename charT> std::basic_istream< charT > & operator>>(std::basic_istream< charT > & is, time_period & tp);
operator>> for time_period. time_period must be in "[date time_duration/date time_duration]" format.
