Get execution time programmatically

[eluser]shakur[/eluser]
Hello guys,

This is my first post so I apologize if this sounds basic or nonsense.
What I basically need is to estimate the execution time without actually displaying the view on the browser. As a matter of fact I wish to estimate execution time of a script that I keep for example in my db, but I'm not sure if this is feasible.

What I have done so far:
1. Retrieved the script from db
2. Created a new CI view from the script
3. Used the $this->load->file('myfile', TRUE); to load the file through the Loader (I guess I could use the $this->load->view here)..
4. Asking for help..

I've used $output = $this->output->get_output(); for getting the loaded file but this wont give me the actual value of {elapsed_time} but the html code.

How can I get the actual value?
Even better is it possible to achieve this without creating files or views and loading them (i.e., is it possible to estimate the execution time of an html string/scrip ?)

Thanks for your time