Option Explicit
Public Next_Timer_Time As Variant

Public Sub Start1() ' запускается при нажатии на кнопку на листе.
        Cells(5, 4).Value = "Ready!!!"
        UserForm1.Show
End Sub

Public Sub Finish1()
Application.OnTime Next_Timer_Time, "my", False
        Unload UserForm1
End Sub

Public Sub my()
Cells(5, 4).Value = "QWERTY!!!"
End Sub

Private Sub CommandButton1_Click()
Module1.Finish1
End Sub

Private Sub UserForm_Activate()
Next_Timer_Time = Now + TimeValue("00:00:10")
Application.OnTime Next_Timer_Time, "my"
End Sub

Private Sub UserForm_QueryClose(Cancel As Integer, CloseMode As Integer)
Module1.Finish1
End Sub

Application.OnTime Next_Timer_Time, "my", False

Application.OnTime Next_Timer_Time, "my", , False

Call Application.OnTime(EarliestTime:=Next_Timer_Time, Procedure:="my", Schedule:=False)