trigger a form submission button using custom cron
This seems a little bit odd. Form submission are meant to be dealt with by humans in order to transfer information to a specific service.

So if you want to send any kind of request to a dedicated service, yes, that is possible using drupal_http_request.


  This is a flexible and powerful HTTP client implementation. Correctly handles GET, POST, PUT or any other HTTP requests. Handles redirects.


If you want to submit a Drupal form on cron, then you can use drupal_form_submit.


  This function allows you to supply values for form elements and submit a form for processing. Compare to drupal_get_form(), which also builds and processes a form, but does not allow you to supply values.


If you want to execute any custom logic (which might also be the result of a form submission by humans) then this is also possible using custom code.

For all that, you will need to implement hook_cron() in a custom module.

If anything else, please elaborate on what it is that you want to achieve.