Same on my 2008 650GS. I understand that there is a small battery (or capacitor?) which powers the clock and a few ofther electronics on the dash which charges when you ride. This is so that you dont have to re-set everything if the main bike battery is disconnected. My bike was not run for a few years and this small battery obviosly ran flat and now does not hold a charge. As with yours if I re-set the clock and then ride it keeps time. Will also keep time for about a day or so but then goes flat again. I dont know if the battery can be changed and I have kicked myself a few times as I had the clocks off and stripped down to replaced the dial which was in kms. Should have looked then.