Disclaimer: I do not work for Marketo Engineering (the development group) therefore I can share few ideas based on my development roles in the free open source software movement. The opinions expressed are my own and do not necessarily reflect those of Marketo.
In general that is a server-side code. JavaScript would pause at browser-side and that is not exactly the goal you may have in mind.
Pausing a flow is normally accomplished timestamping a record and then running a scheduled task to scan the table for records reaching that timestamp.
In the Linux/Apache/MySQL/PHP stack that usually done by a cron job starting a PHP script. (Marketo runs on LAMP).
In SugarCRM the crontab looks like
* * * * * cd /var/www/html/sugar && /usr/bin/php -f cron.php 2>&1
Apple has introduced a resource called launchd, which includes cron-like functionality, though it is broader in scope. The control file is /Library/LaunchDaemons/com.sugarcrm.Scheduler.plist
Changing the default functionality in Marketo would be addressed either through "Ideas" or a customisation managed by Professional Services.
