Big Bend is always a toss of the dice as far as water flow in the canyons is concerned. Especially true for a date set weeks in advance.
Mid to late January may well be better than Feb and for sure March- as far as water flow is concerned.
It all depends on weather tho, a major storm can come thru with little if any notice.
I was down there one year in winter, went to bed after setting around a camp fire in shirt sleeves, woke up in the early AM to horizontal snow and sleet beating on the tent, Rio flashed a foot or so higher. Snowed all next day. Late afternoon sun came out, next day sunny and in the 70-s You never know.