Whitish smoke implies water getting into the combustion chamber. That could be a head gasket. However, the colour is often very hard to discern from inside a vehicle. Since you mention that you aren't loosing fluids, I would lean toward oil-based smoke. Just a few drops of oil make a lot of smoke. The smell would actually tell you more.
If it is oil, I would suspect valve stem seals before rings. The primary reason is that it is occurring after the car has sat long enough to cool down. This is when a drop or two drips down into the combustion chamber. When you start the car this is quickly burnt up and, in the process, is fouling your plugs some. That will clear up as the oil is burnt off and then the car will run fine again. As the seals get worse, the quantity of oil will increase and, eventually, the oil will completely foul the plugs out. At that point, the car may not start until the plugs are cleaned/changed (I know from personal experience).
I would suggest you do a compression test and possibly buy a kit to test for combustion gasses in the coolant. Regardless, the standard repair calls for pulling the head and that means you should replace stem seals and the head gasket at the same time. You can do the stem seals with the head on, but that requires an air compressor and may require a special tool to compress the springs. If your timing belt and water pump are fairly new, I would try it with the head still on. If they need replacing, it's really fairly simple to pull the head on a 4 cylinder.