Can't update LABEL text on kivy file

Question

I have a problem with updating a label text: id: time_ // the strange thing is , i can read(print) with self.ids.time_.text. Merci for help

class Scroll(Screen):
    def __init__(self, **kwargs):
        super(Scroll, self).__init__(**kwargs)
        self.sec = 0
        self.min = 0
 
    def Label_updater(self,time):    
        print(self.ids.time_.text)
        #self.ids.time_.text= str(time)
        self.ids.time_.text='new_ text'

    def start_timer(self, *args):
        self.sec += 1
        self.time = f'00:0{self.sec}'
        self.Label_updater(self.time)
        
    def on_start(self):
        Clock.schedule_interval(self.start_timer, 1)

kivy file :

<Scroll>: 
    id: scroll_id     
    canvas:
        Color:
            rgba: 149 / 250.0, 77 / 250.0, 114 / 250.0, 0.9
        Rectangle:
            pos: self.pos
            size: self.size
    BoxLayout:
        spacing:7    
        padding:10
        size_hint:(1,0.1)
        pos_hint:{'top':1,'b':1}
        
        Label:
            id: score
            text: 'Score: 00'
        Label:
            id: level
            text: 'Level: 01'
        Label:
            id: time_
            size_hint: (1.0, 0.83)
            text: '00:00'
            color: 'red'
     


    BoxLayout:
        size_hint:(1,0.9)
        GamePage:
            padding: 20,20,20,20

---

will try to explain the probleme with some pictures in class GamePage i did create some Buttons with callback = pressed( ) in pressed from there u see the starter object activating start_timer() (( this will start the timer ))
enter image description here enter image description here when i push a Button ---> everything is working fine till i can print(self.ids.time_.text) and i see in logfile the timer working but in the screen the Label text still 00:00

enter image description here

but if i press the button ( added from the kivy file ) everything is working fine

i want to start the timer when i push any button enter image description here