Sub Demo()
Dim Rng As Range, Start
Const Pause As Long = 2    ' Set duration.
Recycle:
With ActiveDocument.Range
  Set Rng = .Characters.First
  Do
    Start = Timer
    Do While Timer < Start + Pause
      DoEvents    ' Yield to other processes.
    Loop
    Set Rng = Rng.GoTo(What:=wdGoToBookmark, Name:="\Line")
    If Rng.End = .End - 1 Then GoTo Recycle
    With Rng
      .Collapse wdCollapseEnd
      .Select
    End With
  Loop
End With
End Sub