Setting textblock margin based on content size

I am trying to show the overall progress of current playing song in below format.

hh:mm:ss / hh:mm:ss ---> current time in hh:mm:ss / total time in hh:mm:ss

<Border Margin="30,0,20,0" Name="NowPlayingScurbberPanel" RelativePanel.AlignLeftWithPanel="True" RelativePanel.AlignRightWithPanel="True" RelativePanel.Below="NowPlayingButtonPanel" RelativePanel.AlignBottomWithPanel="True">
                                    <StackPanel Visibility="{Binding Path=ShouldProgressBarBeVisible, Converter={StaticResource BoolToVisibilityConverter}}" MinHeight="40">
                                        <Grid>
                                            <Grid.RowDefinitions>
                                                <RowDefinition Height="Auto" />
                                                <RowDefinition Height="*" />
                                            </Grid.RowDefinitions>
                                            <TextBlock x:Uid="NowPlayingCurrentMediaTimeText" Margin="0,0,80,30" Style="{StaticResource NowPlayingMediaTimeStyle}" Grid.Row="0" Text="{Binding Path=DisplayedMediaTimeCurrent}" HorizontalAlignment="Right" />
                                            <TextBlock x:Uid="slash" Margin="0,0,60,30" Style="{StaticResource NowPlayingMediaTimeStyle}" Grid.Row="0" Text=" / " HorizontalAlignment="Right"  />
                                            <Slider x:Uid="NowPlayingScrubber" Margin="0,20,0,0" Style="{StaticResource NowPlayingMediaScrubberStyle}" Grid.Column="1" x:Name="NowPlayingScrubber" Value="{Binding Path=ProgressBarPercentage, Mode=TwoWay}" DragStarting="OnScrubberDragStarted" DropCompleted="OnScrubberDragCompleted" ValueChanged="OnScrubberDragDelta" IsEnabled="{Binding Path=ScrubberEnabled}"  />
                                            <TextBlock x:Uid="NowPlayingTotalMediaTimeText" Margin="60,0,0,30" Style="{StaticResource NowPlayingMediaTimeStyle}" Grid.Row="0" Text="{Binding Path=DisplayedMediaTimeTotal}" HorizontalAlignment="Right"  />
                                        </Grid>
                                    </StackPanel>
                                </Border>

Things are working fine if total and current played time in less than an hour but when it cross more than a hour than "Slash" overlap with total time. If i give additional margin then content with less than an hour time looks bad.

How can i give margin based on content length or is there any better solution to solve this problem.

Thanks

#xaml