You can look at the extension DateTimePicker
I've tried not to use the extension and I get to see the time, but I can not select it so it always puts you at 00:00.
I leave the code in case it can help you:
<DatePicker x:Name="dpFirst" HorizontalAlignment="Left" Margin="5,29,0,0" VerticalAlignment="Top" DisplayDate="2018-06-18" SelectedDateFormat="Short" Width="181">
<DatePicker.Resources>
<Style TargetType="{x:Type DatePickerTextBox}">
<Setter Property="Control.Template">
<Setter.Value>
<ControlTemplate>
<TextBox x:Name="PART_TextBox"
Text="{Binding Path=SelectedDate, StringFormat='yyyy-MM-dd HH:mm',
RelativeSource={RelativeSource AncestorType={x:Type DatePicker}}}" />
</ControlTemplate>
</Setter.Value>
</Setter>
</Style>
</DatePicker.Resources>
</DatePicker>
Greetings