If your bush is still dormant, you should not have to worry. If it's begun to leaf out, the frost might nip the new growth--a light horticultural cloth around the bush will proect it--but it should be just fine.

Here is a link that might be useful: HarvestToTable.com

Let it be. Blueberries are extremely cold hardy, even the evergreen forms, and none are likely to be leafing out in January :-) Your only concern regarding frosts/freezing for hardy plants in containers is when it gets cold enough to freeze the soil mass solid. Plant roots tend to be around 20 degrees less hardy than the top growth and can more easily be permanently damaged when container soil is frozen.