SRB600-Lab2 -J values in .rpmmacros

I did this Lab. I was used in my lab top and used fedora13.
This output rebuilding a package to base -j value
I installed and rebuild software mediawiki.
This source size was
-rw-r--r--. 1 ycshon ycshon 11528751 Jul 5 15:05 mediawiki-1.15.4-54.fc13.src.rpm
[root@localhost ~]# cat ~/.rpmmacros
%_topdir %(echo $HOME)/rpmbuild
%_smp_mflags -j1--> Change value 1 to 5
%__arch_install_post /usr/lib/rpm/check-rpaths /usr/lib/rpm/check-buildroot


-j1
real 1m3.124s
user 0m43.467s
sys 0m19.241s
-j2
real 1m5.417s
user 0m44.490s
sys 0m21.499s
-j3
real 1m7.819s
user 0m44.787s
sys 0m23.487s
-j4
real 1m8.440s
user 0m45.184s
sys 0m24.231s
-j5
real 1m9.077s
user 0m45.641s
sys 0m25.203s
So, if rebuild software, j1 value was more faster then other value.