Reason for the Delay:
In order to avoid the delay we have to execute our function "onload" event of any control and following steps can be considered to achieve this functionality.
// My method logic
2.Create a "img" element anywhere on your page(Since we can not capture "onload event" of most of the controls).
3. Set the image source to "/_layouts/images/blank.gif" so that nothing is visible on the page.
<IMG SRC="/_layouts/images/blank.gif" width="1" height="18" onload="MyMethod();"/>
Note: Mentioned issue is quite visible in case you are trying to hide/show some buttons/controls of the page on load of the page.