Multiple processors

We have a partition which runs *one* batch job and one interactive session 
for the operator that checks on the batch job occasionally.  This batch job 
runs for days at a time and when it finishes, another similar job is kicked 
off by the operator.  We want to reduce the run time of the batch job.  One 
suggestion is to add another processor to the partition.  I'm not convinced 
that adding another processor will improve the run time.  So my dumb 
question for today is:

Will adding another processor to a partition running a single batch job 
decrease the run time of the batch job?

Thanks,

Steve