Re: Is it too late?
it could be that if it was too cold to inspect, and too cold for the bees to fly, the syrup in the feeder was also too cold for the bees to take.
foraging is just now starting in earnest here in the south east. they should be bringing in pollen and nectar from the maples and elms. the forecast looks good, and there will be more and more blooms.
if they are bringing in a lot, i don't think they will starve.
an alternative to the top feeder is an inexpensive quail feeder or chicken waterer. you can put it outside on the warm flying days and they can get a lot in a short amount time.
sounds like you made a good move reducing the volume and putting the beetle traps in.
journaling the growth of a treatment free apiary started in 2010. 20+/- hives