Put the grid in a ScrollViewer. Do not set the Height on the timeGrid
<ScrollViewer>
<Grid Name="TimeGrid" HorizontalAlignment="Left" ShowGridLines="False" Margin="10,44,0,0" VerticalAlignment="Top" Width="772">
<Grid.ColumnDefinitions>
<ColumnDefinition/>
<ColumnDefinition/>
<ColumnDefinition/>
<ColumnDefinition/>
<ColumnDefinition/>
<ColumnDefinition/>
</Grid.ColumnDefinitions>
</Grid>
</ScrollViewer>