Hi Ed, I would wait til early spring. Make sure there is plenty of honey & pollen coming in. Pick a nice warm day & try to do the split before the bees start preparing to swarm.
It all depends on what climate you're in. In a sub-tropical zone where I am, as far as the bees are concerned, Spring starts well before our official Winter ends. Once the days start to lengthen & the flowers are producing lots of pollen, the bees start to work towards swarming.
I try to monitor the hive's populations so I can exercise preemptive swarm control measures.