I don't know the answer to your question regarding Wr fluctuations throughout the year, but my guess is that the yearly Wr would have an envelope of movement to account for pre-spawn, spawn, and winter-bulking-up. So to that degree, yes, it may take a year to be able to compare deltas above and beyond an envelope of weight variation.

However, I think you would start to see general improvements in the LMBs in a few months providing you have enough forage base.

Excerpt from Robert Crais' "The Monkey's Raincoat:"
"She took another microscopic bite of her sandwich, then pushed it away. Maybe she absorbed nutrients from her surroundings."