The days getting longer is one sign the bees see and heed. They will think spring and brood rearing. Here is a bit I posted on my local club board, but thought some here may benefit from it, too. I am in NC, so adjust to your climate.
""Now is the time to think spring. Walk up to the back of your hive. Take hold of the handle on both sides. Lift. If it is very heavy, all is well. If it is light, think FEED.
Do this once per week. In Feb. or Mar., you will notice it becoming lighter. This is when they can starve. They are feeding 20,000 new babies and the cupboard can become bare quickly.
If you start lifting now, once weekly, by then you will know what it should feel like, and which hives need feed.
CAUTION: Once you start feeding for spring, they will ramp up brooding. They can run out of food and starve the whole hive within 2 to 4 days. NEVER let the feeder get empty once spring feeding has began.""