verifica se anno bisestile,controllo tempi trascorsi, con visual basic

inserire anno, (tempo inizio prova e tempo fine prova)

cliccare ver controllo e calcolo

VERSION 5.00
Begin {C62A69F0-16DC-11CE-9E98-00AA00574A4F} UserForm2 
   Caption         =   "UserForm2"
   ClientHeight    =   4560
   ClientLeft      =   45
   ClientTop       =   330
   ClientWidth     =   7545
   OleObjectBlob   =   "bisestile.frx":0000
   StartUpPosition =   1  'CenterOwner
End
Attribute VB_Name = "UserForm2"
Attribute VB_GlobalNameSpace = False
Attribute VB_Creatable = False
Attribute VB_PredeclaredId = True
Attribute VB_Exposed = False
Option Explicit

Private Function bisestile(anno As Integer) As Boolean
Dim d As Date
d = DateSerial(anno, 2, 28)
d = d + 1
If Month(d) = 2 Then
bisestile = True
Else
bisestile = False
End If
CommandButton1.SetFocus
End Function

Private Sub CommandButton1_Click()
Dim anno As Integer
TextBox1.SetFocus
anno = TextBox1.Text
If (bisestile(anno)) Then
Lista.AddItem ("bisestile")
Else
Lista.AddItem ("non bisestile")
End If
TextBox1.SetFocus
TextBox1.Text = ""
End Sub

Private Sub CommandButton2_Click()
Dim x As Date
Dim y As Date
x = TextBox2.Text
y = TextBox3.Text
Lista2.AddItem (secondi(x, y))
End Sub

Public Function secondi(inizio As Date, fine As Date) As Long
Dim differenza As Double
Dim risultato As Double
differenza = (fine - inizio)
risultato = (differenza / 1.15740740741499E-05)
secondi = risultato

End Function
Public Function minuti(inizio As Date, fine As Date) As Long
Dim differenza As Double
Dim risultato As Double
differenza = (fine - inizio)
risultato = (differenza / 0.000694444445)
minuti = risultato

End Function

Private Sub CommandButton3_Click()
Lista2.Clear
End Sub

Private Sub CommandButton4_Click()
Dim x As Date
Dim y As Date
x = TextBox2.Text
y = TextBox3.Text
Lista2.AddItem (minuti(x, y))
End Sub