What command do I use to determine how long my actual boot time is? From the grub screen until all the start up processes are finished in the background. I ask because Launcher stays purple for at least another minute or so after I have desktop use. So, I wait until I see it change to the color that matches the theme in use before I begin my session.
The next logical step would be to analyse the boot time data, determine if there are errors, fix, and stream line it.
Generally 'dmesg' has the seconds-since-boot time stamp in the left hand column. So 'dmesg | head' should show that all the first events occurred within 0.000000 seconds since the kernel started. Running 'dmesg | tail' immediately after you login should give a pretty good idea. /var/log/kern.log has this same info but each seconds-since-boot stamp is accompanied by the system time as well, so logging in, running 'date' and doing some arithmetic will give you a what might be a more reliable approximation, depending on exactly what you're looking for. The number you're looking for is subject to interpretation. You may be looking for the time it takes before you are given a login prompt, or the time it takes between startup and running your first interactive command, or you may want to know how much time passes before init starts and this gives you a chance to run user-space code via the startup scripts, etc.
You might want to take a look at BootChart. It has probably more features than you need, but from what I remember has what you are looking for.
http://ccm.net/faq/4268-ubuntu-monitor-your-boot-sequence-with-bootchart
Type in console;
last -x | grep boot
and also you may want to use;
last -x | grep shutdown last -x | grep reboot
For boot inf;
cat var/log/boot.log or less var/log/boot.log