Hide the nanosleep time tuning behind #ifdef TUNETIME
Hide the nanosleep time tuning behind #ifdef TUNETIME

In practice it does not have a noticable effect (maybe due to nanosleep()
sleeping for *at least* the specified time) so it mostly complicates code.

While here show negative values for twait, they sometimes happen.

rene0/dcf77pi,rene0/dcf77pi