WordPress API's and admin loading time

In a regular WordPress install update checks should be cached for 12 hours. If that’s not happening for you and you’re seeing these requests on *every* admin page load, then something is preventing them from being cached, could be your theme, could be a plugin, could be a server configuration.

With regards to cron, indeed spawning it will take up a second, but note that it should not be spawned on every request. I recommend you look into using your system’s crond to invoke cron, and disable WordPress from spawning it via a wp-config.php directive:

define( 'DISABLE_WP_CRON', 'true' );