async openPicker() {
      this.tempValue = this.value && this.isValid(this.value) ? this.value : this.getFormat().format(new Date());
      const responsivePopover = await this._getPopover();
      responsivePopover.showAt(this);
    }
Opens the picker.
@async
@public
@method
@name sap.ui.webc.main.TimePickerBase#openPicker
@returns {Promise} Resolves when the picker is open