Depending on your version of Boost:
Either…
#include <boost/chrono.hpp>
#include <boost/thread/thread.hpp>
boost::this_thread::sleep_for(boost::chrono::milliseconds(100));
Or…
#include <boost/date_time/posix_time/posix_time.hpp>
#include <boost/thread/thread.hpp>
boost::this_thread::sleep(boost::posix_time::milliseconds(100));
You can also use microseconds, seconds, minutes, hours and maybe some others, I’m not sure.