Public Class Form1


    Private preDate As DateTime
    Private Sub Form1_Load(sender As Object, e As EventArgs) Handles MyBase.Load
        DateTimePicker1.Format = DateTimePickerFormat.Custom
        DateTimePicker1.CustomFormat = "HH:mm"
        preDate = DateTimePicker1.Value
    End Sub




    Private Sub DateTimePicker1_ValueChanged(ByVal sender As Object, ByVal e As System.EventArgs) Handles DateTimePicker1.ValueChanged
        Dim differenza As Long = DateDiff(DateInterval.Minute, preDate, DateTimePicker1.Value)
        Dim bool As Boolean = False 'negativo
        If differenza > 0 Then
            bool = True 'positivo
        End If

        If DateTimePicker1.Value.Minute = 59 Then
            If bool = True Then 'Positivo 59-0 = -59
                If preDate.Minute = 0 Then
                    DateTimePicker1.Value = DateTimePicker1.Value.AddHours(-1)
                End If
            End If
        End If

        If DateTimePicker1.Value.Minute = 0 Then
            If bool = False Then 'negativo 
                If preDate.Minute = 59 Then
                    DateTimePicker1.Value = DateTimePicker1.Value.AddHours(1)
                End If
            End If
        End If

        preDate = DateTimePicker1.Value
    End Sub
End Class