Button Click if determined

Basically I need to check a particluar frame on a webpage for the presence of a button (which isn't always there), at a predefined user time interval, details of which I have from the source of the frame...see below... <input type="button" class='Button_Check' name="btnCheck" value="Click This" onClick="[login to view URL]();"> If the button isn't there check again for button at a predefined user interval, if it is there I need to automatically click it and stop the loop. Thanks