Hi Roberto,

You have to re-template the DayViewTimeslotHeader, adding a TextBlock bound to the Start.Minute property of the DayViewTimeslotHeader.
  <TextBlock Text="{Binding Path=Start.Minute, Mode=OneWay, RelativeSource={RelativeSource TemplatedParent}}"
                                           Foreground="{TemplateBinding ComputedForeground}"
                                           Visibility="{Binding Path=LeadingTickmarkKind, RelativeSource={RelativeSource TemplatedParent}, Converter={StaticResource tsTickmarkKindToVisibilityNotConverter}}"
                                           HorizontalAlignment="Right" Margin="0,3,7,0"></TextBlock>
I attached the sample application.

Thanks,
Diyan Dimitrov