See the #if below. I'm pretty sure these should do the same thing. The expires_from_now() version does what I'd expect and calls onTimer() once a second. The expires_at() version never calls onTimer(). Even though 'expires_at() const' returns 1s from now: doit now =2010-May-21 15:07:24.882854 expires_at =2010-May-21 15:07:25.882854 <and nothing more> //********************************************************************** *********** #include <boost/asio.hpp> #include <boost/date_time/posix_time/posix_time.hpp> #include <iostream> using std::cout; using namespace boost::asio; using namespace boost::posix_time; io_service ioService; deadline_timer timer(ioService); seconds s1(1); void doit(); void onTimer(const boost::system::error_code&){ doit(); //repeat forever } void doit(){ ptime now=microsec_clock::local_time(); cout<< "doit now ="<< now <<std::endl; #if 0 timer.expires_from_now(s1); //works #else timer.expires_at( now+s1); //doesn't work #endif timer.async_wait( onTimer ); cout<< "expires_at ="<< timer.expires_at()<< std::endl ; } void timerTest(){ doit(); io_service::work w(ioService); ioService.run(); } int main(){ timerTest(); return 0; }