About 1 every couple of days. I have loads and loads, assuming I haven't been screwed by villagers. Still nothing. :/
That's a strong assumption.
BTW, is the number really so important? I'm watering only the flowers I want to hybridize (around 40), and I'm getting 2-3 hybrids a day. I don't think you can get more than that, Am I mistaken?
I'm doing orange cosmos / orange cosmos, blue pansies / blue pansies and red* rose / red* rose. The main issue is that most of the time, I get "common" flowers, such as basic or pink cosmos, red* or purple rose, etc.
I even thought to try to water only three pairs of chosen flowers. The only problem with that is the villagers. They sometimes water random flowers. I usually remove those, but I can miss some of them. With a lower number of watered flower, I fear that villagers flowers could "win" more often.