Sub StartBlink()
With ThisWorkbook.Worksheets("Лист1").Range("O8").Font
        If .ColorIndex =  3  Then ' Red Text
            .ColorIndex =  9  ' Black Text
        Else
            .ColorIndex =  3  ' Red Text
        End If
    End With
    RunWhen = Now + TimeSerial( 0 ,  0 ,  1 )
    Application.OnTime RunWhen, "'" & ThisWorkbook.Name & "'!StartBlink", , True
End Sub

Sub StopBlink()
With ThisWorkbook.Worksheets("Лист1").Range("O8").Font.ColorIndex = xlColorIndexAutomatic
    RunWhen = Now + TimeSerial( 0 ,  0 ,  1 )
    Application.OnTime RunWhen, "'" & ThisWorkbook.Name & "'!StartBlink", , False
End With
End Sub

Sub StartBlink()

Dim w As Range
For Each w In ThisWorkbook.Worksheets("Лист1").Range("O7:O50")
  If w.Value = "t истекло" Then
    With w.Font
        If .ColorIndex =  3  Then ' Red Text
            .ColorIndex =  9  ' Black Text
        Else
            .ColorIndex =  3  ' Red Text
        End If
    End With
  End If
Next
RunWhen = Now + TimeSerial( 0 ,  0 ,  1 )
Application.OnTime RunWhen, "'" & ThisWorkbook.Name & "'!StartBlink", , True

End Sub