open() {
const amazingTimePicker = this.atp.open({
  theme: 'material-orange',
  time:this.Start
});
amazingTimePicker.afterClose().subscribe(time => {
    this.Start = time;
    this.onchange()
});
}

<input disabled   theme="material-orange" type="time" matInput class="material" atp-time-picker value="{{Start}}"/>