Chrysanthemums are hardy, so I'd simply plant it in the garden and let it go. (Protect from slugs when it starts into growth in spring.) It will flower in the autumn like other garden chrysanthemums - commercial growers get them to flower at other times of year by submitting them to a rigid regime of light and dark that fools them into thinking it's late summer when it's not

I did this 5 yrs ago and they are doing realy well. often the pot ones are 3 or 4 small plants. I split mine up. cheap plants :o)

A few of the largest florist's varieties may wait until too late into the winter to bloom, but there's only one way to find out--plant it out!