When the polar ice caps melt, the north polar ice cap would not have much effect, because it is floating sea ice. The ice caps that would matter are the Antarctica and Greenland ice caps. If they wave to melt, days would get slightly longer (and there would be slightly fewer of them in a year). This is because the liquid water would distribute more evenly about the globe rather than all being near the poles, so the earth's moment of inertia would increase.
Since, the earth's angular momentum will not change, that means that its angular velocity (rate of turning) would decrease.