Or using a 'flag' to detect a change in the input and run the function. 
 
 #include <Date.au3>
#include <EditConstants.au3>
#include <GUIConstantsEx.au3>
#include <WinAPI.au3>
#include <WindowsConstants.au3>
Global $__iLabel = -9999, $__iFlag = 0
Example()
Func Example()
	Local $hGUI = GUICreate('Input Filter', 300, 30)
	$__iLabel = GUICtrlCreateInput('', 5, 5, 290)
	GUIRegisterMsg($WM_COMMAND, 'WM_COMMAND')
	GUISetState(@SW_SHOW)
	While 1
		If $__iFlag Then
			$__iFlag = 0
			_Change()
		EndIf
		Switch GUIGetMsg()
			Case $GUI_EVENT_CLOSE
				ExitLoop
		EndSwitch
	WEnd
	GUIDelete($hGUI)
EndFunc   ;==>Example
Func _Change()
	ConsoleWrite('Change: ' & _Now() & @CRLF)
EndFunc   ;==>_Change
Func WM_COMMAND($hWnd, $iMsg, $iwParam, $ilParam)
	#forceref $hWnd, $iMsg, $iwParam, $ilParam
	Local $iLoWord = _WinAPI_LoWord($iwParam)
	Local $iHiWord = _WinAPI_HiWord($iwParam)
	Switch $iLoWord
		Case $__iLabel
			Switch $iHiWord
				Case $EN_CHANGE
					$__iFlag = 1
			EndSwitch
	EndSwitch
EndFunc   ;==>WM_COMMAND