The way things are, they probably will shut it down from top to bottom of the 1st of February, the same day the tribe would stop netting the lower river. I would be shocked to see them close it as early as the 15th of December, as most of the hatchery fish would not be by the nets. Give the tribes to the 10th of February and and they will have had the opportunity to net probably 90% of the hatchery run, while the recs get a fair chance at about 50% or less. The 2016 catch records show this for return cards for the Skookumchuck.
Skookumchuck reported catch 2016
December --29 January -- 125, February ---- 383, March ---1,033
This means about 52% of the skookumchuck's fish are caught in March. It definitely would not be too late to open it up for top end.

For the entire system, about 61% of the reported winter fish were caught after February first, so a January 15th closure would probably knock it down to 30% or less of the normal catch, possibly more if rains don't bring in some early.

Those are just from the 2016 cards. I do not have time to look at a bunch of years, but it appears to be consistent to what I have seen over the years.