You are correct, WordPress checks for updates to core and plugins every 12 hours, but a better way to word it would be: it checks updates if last update was more than 12 hours ago.
The 12 hour setting is hard coded in
The last updated dates are stored in
wp_options table and the options are:
Because this check does not happen precisely after 12 hours, but rather next time the condition is met (at least 12 hours has passed) then you will not miss the update.
If you like this question & answer and want to contribute, then write your question & answer and email to freewebmentor[@]gmail.com. Your question and answer will appear on FreeWebMentor.com and help other developers.