Looks like it's around week three or four of flower (depending on whether you count flower stretch/pre flower) as a rough estimate without knowing the strain.
Flowering plants lap up the water. I'm going through around 3l a day in a 15L pot, and during veg I used next to nothing. Was unexpected how quickly it started drinking during pre flower.
I start feeding from the bottom during flower, as I find it easier to gauge how hungry the soil is by how quickly it drinks the water in the tray. I also find that my plant usually shows stress signs for when I water from the top in large amounts. If I water once every two days from the top, I find the plant droops afterwards for six hours, but the same amount over two days spread out every 8 hours from the bottom seems to keep the plant praying and happy.