Have you tried the period converter script in MT4? It does what you want. Open a 1min chart of the currency pair, attach the script to the chart by dragging and dropping, input your variable, eg 20 gives bars of 1min x 20 - 20min bars. Then go to the file menu, choose open offline and scroll down and you'll find that 20min chart there. I think you can save the settings, but i haven't gotten around to that myself. Hope that helps