How to calculate time difference between two times in VB

The problem is that your shift overlaps two days, with half an hour in the "second day".
so when you just convert a time to a DateTime object, you get the start time after the end time: 00:30 end, 16:30 start.

Then there is the string comparison ... why? Why convert strings to numbers and then back to strings in order to do a numeric comparison?

Instead, consider it as two shifts: 00:00 to 00:30 and 16:30 to 23:59 and compare for both.
The best way to do this is to consider the string starts as "minutes since midnight":
0 to 30, 990 to 1439 and convert the current time to the same thing: 510.
Then check if it is in either of the two shifts or not.

By the way: 08:30 is not in your shift at all ... so "time expired" would be correct...

Your problem is that you set 16:30 to variable dtShifTime, and then you use dtLateTime when comparing.
dtLateTime is not defined in this code.
Use the debugger to see the values of variables at runtime.

Your code do not behave the way you expect, or you don't understand why !

There is an almost universal solution: Run your code on debugger step by step, inspect variables.
The debugger is here to show you what your code is doing and your task is to compare with what it should do.
There is no magic in the debugger, it don't know what your cpde is supposed to do, it don't find bugs, it just help you to by showing you what is going on. When the code don't do what is expected, you are close to a bug.
To see what your code is doing: Just set a breakpoint and see your code performing, the debugger allow you to execute lines 1 by 1 and to inspect variables as it execute.

Debugger - Wikipedia, the free encyclopedia[^]

Mastering Debugging in Visual Studio 2010 - A Beginner's Guide[^]
Basic Debugging with Visual Studio 2010 - YouTube[^]

Visual Basic / Visual Studio Video Tutorial - Basic Debugging - YouTube[^]
Visual Basic .NET programming for Beginners - Breakpoints and Debugging Tools[^]

Debugging in Excel VBA - EASY Excel Macros[^]
MS Excel 2013: VBA Debugging Introduction[^]
How to debug Excel VBA - YouTube[^]

The debugger is here to only show you what your code is doing and your task is to compare with what it should do.

Quote:

I'm already using debugger for find How the code works but i've no idea for which condition to check Time difference because some condtitions applied

Since you work on hours only, you have a set of condition in the day, and another one when you change of day in the shift.

Try this block of code ... This uses a timespan instance to check for lateness in minutes

Private Sub LatenessCheck()
      Dim dtShifTime As DateTime = Nothing
      Dim dtEntryTime As DateTime = Nothing
      Dim spLateness As TimeSpan

      If Date.TryParse("2019-01-01 16:30", dtShifTime) Then
        'dtShifTime is assigned
      End If
      If Date.TryParse("2019-01-01 08:30", dtEntryTime) Then
        'dtEntryTime is assigned
      End If
      If Not (dtShifTime = Nothing Or dtEntryTime = Nothing) Then
        spLateness = dtShifTime - dtEntryTime
        If spLateness.Minutes < 0 Then
          MsgBox("Late", MsgBoxStyle.Information + MsgBoxStyle.OkOnly, "Late")
        End If
      Else
        'not late, or date assignment error
      End If
    End Sub