Banwaves are over with within hours of when they start.
All the detection occurs weeks/months before the banwave, in which Blizzard collects data of all the suspected botting accounts.
Once they gather enough information they initiate the banwave.
When the banwave is initiated, all of the previously flagged accounts from their detection are hit within hours.
After all the accounts that were flagged are hit by the banwave, the banwave "ends" and everything goes back to normal.
After a banwave ends is the absolute best time to bot. After the last banwave (not this last one, but the one before), I made over gold cap on 5 battlechest accounts just farming Halls of Lightning.