I think over-sparging occurs when you sparge once, take the runnings, sparge again, take the runnings, and sparge again trying to get the last of the sugars out. Each time you drain the mash tun you raise the pH. I don't believe that the time has much to do with it. I also don't believe you accomplish very much with a 10 minute dunk sparge. It doesn't take sugar very long to dissolve into hot water. Agitation would be more beneficial. Try it with a cup of tea. Pour your sugar into your tea and let it sit for ten minutes. Try another cup where you pour the sugar in and stir for 30 seconds.