SOLVED!!
I used a Qtimer to interrupt QMainWindow each one second and call to "getStartStatus" method:
self.loadingLabel = QLabel('Starting...', self)
self.loadingLabel.setGeometry(900, 700, 400, 200)
self.loadingLabel.setFont(QFont('Arial', 20))
self.loadingLabel.setStyleSheet('color:#C7BAD0')
self.timerStartStatus = QTimer(self)
self.timerStartStatus.timeout.connect(self.getStartStatus)
self.timerStartStatus.start(1000)