Add simulation start time and duration options
Add simulation start time and duration options

osqzss/gps-sdr-sim,sgk/gps-sdr-sim,andrmarkv/gps-sdr-sim,andrmarkv/gps-sdr-sim,osqzss/gps-sdr-sim,MohammadSecure/GPS-SDR-SIM,andrmarkv/gps-sdr-sim,sgk/gps-sdr-sim,MohammadSecure/GPS-SDR-SIM