Сбивается таймер при отправке писем: интервал не всегда равен установленному

Do
Threading.Thread.Sleep(300000)
Loop

Public Class Timer
    Inherits System.ComponentModel.Component
    Event Tick(sender As Object, e As EventArgs)
    Private Thread As Threading.Thread
    Private Current As Threading.SynchronizationContext
 
    Sub New()
        Current = Threading.SynchronizationContext.Current
    End Sub
 
    Public Overridable Sub Start()
        If Not Thread Is Nothing Then [Stop]()
        Thread = New Threading.Thread(AddressOf OnEventTick)
        With Thread
            .SetApartmentState(Threading.ApartmentState.MTA)
            .IsBackground = True
            .Start()
        End With
    End Sub
 
    Public Overridable Sub [Stop]()
        If Not Thread Is Nothing Then
            Thread.Abort()
            Thread = Nothing
        End If
    End Sub
 
    Public Overridable Property Interval As TimeSpan = New TimeSpan(1000)
 
    Private Sub OnEventTick()
        Do
            Threading.Thread.Sleep(Interval)
            Current.Post(AddressOf Post_EventTick, Nothing)
        Loop
    End Sub
 
    Private Sub Post_EventTick()
        RaiseEvent Tick(Me, New EventArgs)
    End Sub
End Class