  We present optimized implementations of the weak-coupling continuous-time
Monte Carlo method defined for nonequilibrium problems on the Keldysh contour.
We describe and compare two methods of preparing the system before beginning
the real-time calculation: the "interaction quench" and the "voltage quench",
which are found to be suitable for large and small voltage biasses,
respectively. We also discuss technical optimizations which increase the
efficiency of the real-time measurements. The methods allow the accurate
simulation of transport through quantum dots over wider interaction ranges and
longer times than have heretofore been possible. The current-voltage
characteristics of the particle-hole symmetric Anderson impurity model is
presented for interactions U up to 10 times the intrinsic level width Gamma. We
compare the Monte Carlo results to fourth order perturbation theory, finding
that perturbation theory begins to fail at U/Gamma>4. Within the parameter
range studied we find no evidence for a splitting of the Kondo resonance due to
the applied voltage. The interplay of voltage and temperature and the Coulomb
blockade conductance regime are studied.
