Please note that official support for this menu version has now ceased. There are still plenty of users, though, and the forum is still running. Some of our long-time users may be able to help you out.
This, as you have probably assumed is because of the PlaceMenu() function.
The reason it waits is because Tables need to generated fully before they are rendered to the screen and it's at this point only that the menu system knows where the menu should go.
What I suggest is try setting a Top and a Left value for the menu as close as you can get to where the menu will be placed.
Better sill try and get your menu positioned properly without the use of PlaceMenu() with a combination of Screen Position and offsets.