Something is amiss in my timespan code - vb.net

Question

My code is as follows:
Private Sub tbRcvrDepartTime_textchanged(sender As Object, e As EventArgs) Handles tbRcvrDepartTime.TextChanged
'Converts the 90 Receiver Arrival & Departures Date & Times to a string for comparison
Dim raTime As String = tbRcvrArriveTime.Text 'Takes the Time only String and converts to string
Dim raDate As String = dpRcvrArriveDate.Text 'Takes the DateTimePicker and converts date to string
Dim raDateString = String.Concat(raDate, " ", raTime) 'Puts together the Date & Time into one continuous string
'Dim raDateFormat As String = "MM-dd-yyyy HH:mm" 'Sets the String to Date style Format
Dim raResultDate As Date = CDate(raDateString) 'Finalizes the String for use in below comparison
Dim rdTime As String = tbRcvrDepartTime.Text 'Takes the Time only String and converts to string
Dim rdDate As String = dpRcvrDepartDate.Text 'Takes the DateTimePicker and converts date to string
Dim rdDateString = String.Concat(rdDate, " ", rdTime) 'Puts together the Date & Time into one continuous string
'Dim rdDateFormat As String = "MM-dd-yyyy HH:mm" 'Sets the String to Date Format
Dim rdResultDate As Date = CDate(rdDateString) 'Finalizes the String for use in below comparison
'Checks to see if 2 or more hours have elapsed since Receiver Arrival/Departure Date & Time
Dim elapsedR As TimeSpan = rdResultDate.Subtract(raResultDate)
tbRcvrDepartTime.BackColor = If(elapsedR.TotalMinutes > 120, Color.LightPink, Color.White)
End Sub
Both raTime & rdTime are separate textboxes.
Both raDate & rdDate are datetimepickers.
When I run the code "live" initially the first record I look at is displayed correctly. Once I move to another record, this goes out the window... I get random results where it will not change the backcolor to the proper color if >120 minutes has elapsed. Other times it changes the backcolor when there is <120 minutes elapsed. Sometimes no change in backcolor when it should or it will change color when it should not. I attempted to originally do this using TotalHours but met with the same results. It is random and is not consistent. I have worked on this for 2 days now with no difference in results. My thinking is there needs to be a way to "refresh" the rdResultDate & raResultDate info when each new record is loaded but I am unable to do that with my code knowledge.
The code must be able to take into account if a new date is present - ie raDate: 11/01/2016 and raTime: 23:46 and
rdDate: 11/02/2016 and rdTime: 03:00 - this would exceed 2 hours (or 120 minutes) and should read "True" and change the backcolor as it is over 2 hours (or 120 minutes).
However if the following were true:
raDate: 11/01/2016 and raTime: 23:46 and
rdDate: 11/02/2016 and rdTime: 01:00 this would not exceed 2 hours (or 120 minutes) and should read "False" and would not change the backcolor.

Answer 1

All of this code:
Dim Detention90 As String
Try
If elapsedR.TotalMinutes > 120 Then
Detention90 = "True"
Else
Detention90 = "False"
End If
Select Case Detention90.ToString
Case = "True" : tbRcvrDepartTime.BackColor = Color.LightPink
Case Else : tbRcvrDepartTime.BackColor = Color.White
End Select
Catch ex As Exception
'If a problem occurs, show Error message box
MessageBox.Show("Receiver Arrive Time & Depart Time Elapsed error" & vbCrLf & "Lines 1424-1434")
End Try
condenses down to just this:
Dim elapsedR As TimeSpan = rdResultDate.Subtract(raResultDate)
tbRcvrDepartTime.BackColor = If(elapsedR.TotalMinutes > 120, Color.LightPink, Color.White)
Not sure if it will directly address your issue, but it was a bit too much for a comment and I've found compacting code in this way is often extremely beneficial for tracking down difficult bugs.
But in this case, I suspect the main issue is parsing the datetime values... that you're not always parsing the DateTime value you expect from a given input string. Specifically, you have format string variables raDateFormat and rdDateFormat, but then call Date.Parse() such that these format variables are never used, and you are left at the mercy of whatever the default date format is for your thread, process, or system. If you're on a system that uses a d/m/y order as in the UK instead of the US-style m/d/y, you'll end up with some strange results. You probably want DateTime.ParseExact() instead.