Writing to a cell in a loop

[SamT]

Try this

Sub TimeChanger()
Dim i as Long
Dim LR As Long
Dim X As String

With Sheets("Sheet2")
   LR = .Cells(Rows.Count, "A").End(xlUp).Row
    For i = 4 To LR 
        X = .Cells(i, "A").Value2 
        If CInt(Left(X, 2)) > 24 Then _
       .Cells(i, "A")) = CStr(CInt(Left(X, 2)) Mod 24) & Mid(X, 3)
    Next
End If
End Sub