Comparing start time is greater than End time WPF datepicker

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C#

WPF

I have a RadTimePicker and i have start time and end time.I have to compare if start is greater than the end time or not.I am using WPF with MVVM.

<telerik:RadTimePicker  HorizontalAlignment="Center"
                                                             VerticalAlignment="Center" Height="Auto" Width="Auto"
                                                             DisplayFormat="Long"  removed="LightYellow" SelectedValue="{Binding PeriodSelected.StartTime.Time}"
                                                             FontSize="12"/>

<telerik:RadTimePicker  HorizontalAlignment="Center"
                                                              VerticalAlignment="Center" Height="Auto" Width="Auto"
                                                              DisplayFormat="Long"  Background="LightYellow"
                                                              SelectedValue="{Binding PeriodSelected.EndTime.Time}"
                                                              FontSize="12"/>

public EP_TimeBase StartTime
     {
         get
         {
             return _startTime;
         }
         set
         {
             _startTime = value;
             RaisePropertyChanged("StartTime");
         }
     }

     private EP_TimeBase _endTime;
     public EP_TimeBase EndTime
     {
         get
         {
             return _endTime;
         }
         set
         {
             _endTime = value;
             RaisePropertyChanged("EndTime");
         }
     }