SetWinDelay to match parent GUI's time?

[Cuadrix]

I have two GUI's, one parent GUI and one child GUI.
The problem is that, when I launch the script, the parent GUI always takes less time to become visible.
There is about 100ms difference in their "loading time".
How can I make the child GUI appear at the exact SAME time when the parent GUI is launched?
I put SetWinDelay -1 on top BEFORE the child GUI, but nothing changed..