Base Priority and MessageBox TimeOut

1- What am I missing ?
The base priority doesn´t work. Keeps set to normal.(8)
I want idle priority.

OutFile "Fazer_Bcup_Oficina.exe"
Name "BackUp"
!include ${NSISDIR}\Include\WinMessages.nsh
SilentInstall Silent
Page instfiles
!define IDLE_PRIORITY_CLASS 0x00000040

Section...
____________________________________________________
2- How can I set a timeout to a MessageBox MBOK that is
not pressed for ... seconds or minutes?

Oh, I see. I was missing
System::Call "kernel32::GetCurrentProcess() i .s"
System::Call "kernel32::SetPriorityClass(i s, i 0x00000040)"

But the MB_OK timeout is still misterious.

You could manually call the undocumented MessageBoxTimeout using the System plug-in.

System::Call `user32::MessageBoxTimeoutA(i $HWNDPARENT, \

  t 'some message', \

  t 'title', \

  i 0, i 0, i 2000)`