Option Explicit

Declare Function SetTimer Lib "user32" (ByVal hwnd As Long, ByVal nIDEvent As Long, ByVal uElapse As Long, ByVal lpTimerFunc As Long) As Long
Declare Function KillTimer Lib "user32" (ByVal hwnd As Long, ByVal nIDEvent As Long) As Long

Public Sub TimerProc(ByVal hwnd As Long, ByVal uMsg As Long, ByVal idEvent As Long, ByVal dwTime As Long)
    MsgBox Now()
End Sub

Option Explicit

Dim lngTimerID As Long
Dim BlnTimer As Boolean

Private Sub Form_Load()
    BlnTimer = False
    Command1.Caption = "定时开始"
End Sub

Private Sub Form_Unload(Cancel As Integer)
    KillTimer 0, lngTimerID
End Sub

Private Sub Command1_Click()
    If BlnTimer = False Then
        '每5秒钟调用一次函数
        lngTimerID = SetTimer(0, 0, 5000, AddressOf TimerProc)
        BlnTimer = True
        Command1.Caption = "定时结束"
    Else
        KillTimer 0, lngTimerID
        BlnTimer = False
        Command1.Caption = "定时开始"
    End If
End Sub