Before the wait command was modified, I had edited the source myself to use usleep, I took it from smallbasic as shown here after a check for palmos
#elif defined(_Win32)
Sleep(ms);
#elif defined(_DOS)
delay(ms);
#else // Unix
usleep(ms * 1000);
#endif
Yabasic uses the same excluding palmos and dos.
I only know about linux, but it appears the thread is suspended and cpu use falls to near zero. In all cases Control C will not break if done in the graphic window, but does in a terminal if the program was launched from one.
Mind you, most delays are in the ms range rather than seconds, so breaking out is not really a problem.