Depends where you live. A good rule of thumb is to add supplements about three weeks before real pollen is expected to come into the hives and then feed continuously until the weather is very settled and nectar and pollen is coming in steadily.
After Christmas, the queen will be laying already, since queens lay a little all winter, but ramp up when the weather warms and nectar and pollen start to come in.
Some strains of bees respond to feeding more than others. Word is that the Russians are hard to push and will wait for supplies to show up outside the hive, while Italians are willing to build up anytime you can afford to feed them
Feeding patties will ensure a steady supply of protein and maintain the workers in better health and also keep them from ripping out eggs and larvae if you get a cool or rainy spell.
If you want to stimulate brood rearing, then feeding 50/50 syrup in addition to patties helps.
Over stimulating bees too early can be hard on them, though, if there is nothing outside for them and there is not good flying weather.