If i understand correctly you want to have your cron job run every 10 mins. It depends on how Simple’s API is set up…are they using the real cron or wp-cron? If they are using wp-cron the Marko is correct that it will be dependent on when visitors arrive.
Let’s assume Simple’s API is using wp-cron. If that is the case then if you use w3 total cache’s “disk enhanced” mode instead of “disk basic” then it serves cached pages for long periods without wp’s involvement. You can use disk basic caching mode and wp-cron will then continue to fire in its usual way.
In your situation it seems more ideal then to use the real cron jobs and disable wp-cron.
Marko has given you the correct cron job to trigger wp-cron every 10 mins. However, you should add the following line into your wp-config.php which will disable wp-cron’s normal behavior of being triggered after a scheduled event has passed then a visitor pops in (which can be more than 10 mins at times, depending on your site activity), since you would be generating your own cron job for it:
define('DISABLE_WP_CRON',true);
So again, this really depends on what Simple is doing but it sounds to me they are using wp-cron and so your solution is to either switch to using w3tc’s disk basic mode and/or setting wp-cron to be run (as a real cron job) for your site every xx mins. You can set this up in your cPanel if you are not comfy working in shell.
