Black Lives Matter. Please consider donating to Black Girls Code today.

Disabled and enable tabs with callback

I have an app where the user gives some input, and the app then loads some data and visualize them in an extra Tab. Because this loading takes some time, I want to disable the Tab until data is loaded. However, this is not working as I was expecting. The Tab is never disabled. Below I provide a minimal example of my callbacks.
The idea is to click the “Fire” button, and then the “Tab two” shout be disabled. After the “do_process” callback is finished, it should be enabled again.
What do I miss that this not work?
Thanks for the help in advance.

import dash
import dash_html_components as html
import dash_core_components as dcc
import time

app = dash.Dash(__name__)

app.layout = html.Div([
        dcc.Tab(label='Tab one', id='tab1'),
        dcc.Tab(label='Tab two', id='tab2')
    html.Button("Fire", id='btn1'),
    dcc.Input(value='', type='hidden', id='start'),
    dcc.Input(value='', type='hidden', id='stop'),

@app.callback(dash.dependencies.Output('start', 'value'),
              [dash.dependencies.Input('btn1', 'n_clicks')])
def start_process(n_clicks):
    return n_clicks

@app.callback(dash.dependencies.Output('stop', 'value'),
              [dash.dependencies.Input('start', 'value')])
def do_process( value):
    return value

@app.callback(dash.dependencies.Output('tab2', 'disabled'),
              [dash.dependencies.Input('start', 'value'), dash.dependencies.Input('stop', 'value')])
def manage_tab(value1, value2):
    ctx = dash.callback_context
    trigger = ctx.triggered[0]['prop_id'].split('.')[0]
    if trigger == 'start':
         return True
    return False

if __name__ == '__main__':