To be clear "start the process " means first seeing any change in the DW (white/gray edges to the plant). I have never seen DW initially killed off (surface cleared) in less than 30 days. That does not mean it is dead as its seeds will float up and start over. That is why , as PF says , you need to keep the ppm up to get those floating seeds. That can easily take another 30 -60 days. Even after that you should be ready to spot treat with contact herbicide to get any residual DW.
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