With modern malts they fully convert in a much faster time frame. look up the specs of the grain you use. Most, if not all of the commercially available malts convert very quickly. so I guess you might be wasting time. it's not a knock, to each their own. If you are growing and malting your own grain then the inconsistencies might deserve a long mash and/or a step mash. Just trying to help out. good luck. I run iodine tests regularly and frequently get complete conversion in 20-30min.
if your long mashes are for another reason other than starch conversion... please enlighten me as I am always interested in learning a new technique. :-)