When you start seeing ice forming and not melting during the day I would think .Since you still have your pump going it will not stay frozen and sun should warm it during the day .Just make sure your filter or waterfall does not freeze up because pond will empty fast
deicer should be installed when there is first chance of ice forming. A ponds surface can freeze solid in only a few hours with the right wind and temp conditions, it only takes a few hours sealed up that the the gases start building up, you want to keep a open hole at all times. Also moving water during freezing temps can cause the deeper water to lose it's thermal layer cooling the water more than needed. Once ice is starting to form it's best to shut down as much surface water flow as possible.