I think it's different for each dog and the environment they're kept in.
For example, Bandit has already completely blown his coat (and looks really rangy right now!
); he lives primarily indoors and so he's exposed to the warm temps inside.
Willow, on the other hand, hasn't even started to blow her coat. But, she's kept primarily outdoors, so she does probably need it still.
I know it took Bandit about 2 - 3 weeks to completely clear out the undercoat, so once the process starts, expect daily brushing for that time period if you want to keep your sanity!
I saved all the hair from Bandit's shedding, and I'm going to spin it into yarn. 
For example, Bandit has already completely blown his coat (and looks really rangy right now!
Willow, on the other hand, hasn't even started to blow her coat. But, she's kept primarily outdoors, so she does probably need it still.
I know it took Bandit about 2 - 3 weeks to completely clear out the undercoat, so once the process starts, expect daily brushing for that time period if you want to keep your sanity!