I would normally be end of feb depending on weather if it got milder cut it a week or 2 short if it's still cold maybe extend it a week or two.
but this winters been cold if your saying back end of jan then your hardly testing your dog this year at this ground was frozen for 2/3 weeks at the start of jan hardly leaves any room for testing hares when there at their best.
still freezing cold just now infact it's started snowing up my way just now be madness to pack away middle of jan