I recommend using the "restart" option. You will create a restart file to be output at a simulation time prior to the end of the wallclock time, or at a particular interval (e.g., every 24 hours simulation time), and then use that restart file to start the model up again from that point.
The first time you run a simulation, you will set restart = .false. and set your restart_interval to something like 1440, which is the minutes in a 24 hour time period. This means you would get a restart file after each 24 hour simulation time period. Then, let's say your wallclock allowed you to run 6 and 1/2 days of simulation time before it stopped, then you would go back in and set the namelist for your next run to restart = .true. and you could keep the restart interval set to 1440. The new (restart) simulation would start from the beginning of the 6th day and continue to run until it stopped again.
You can set restart_interval to whatever time interval you would like - just so long as it would write out a full restart file before stopping. You will not need to re-run real.exe. You will need to modify your namelist to set restart = .true. and the new start date/time information, then re-run wrf.exe. The restart simulation will start from the date/time you set in your namelist.input file - which should correspond to an available restart file's time. You may find this page helpful - this is a practice given to the tutorial students, but you can use it as a guide. You may want to refer back to the single domain case to see how the namelist was set-up for that simulation, and then how it was set up for the restart.