Post-boot and login notification
For OS X system files you cant not determine the end since it keeps working, but if you have start up apps you can do it for those.

For the OS X you could use the first phase of boot process.

it is indicated in the Console as bootlog[0]: BOOT_TIME 1428512373 0

After that the OSX is running mostly customization, like finding and connecting to your network ect..

Or you could move to next stage in the process and monitor the WiFi connection...and so on.

You could use something like this to Monitor Console automatically in Terminal and make sound if certain message comes.

syslog -w|while read l;do [[ $l = *'message text'* ]]&amp;&amp;afplay /System/Library/Sounds/Blow.aiff;done


Replace "message text" with what you want from the Console log as your trigger.