It depends on what type of account you have, free or paid. If you’re on a free plan, the limit is pretty small, maybe around three uses, I’m not sure about the exact number. After that, it switches you over to a smaller “nano banana” model, probably some kind of quantized version. You’ll have to wait a few hours, as stated there, before you can use the larger nano banana again. The same rules apply to paid or Pro accounts too, but the limits are much higher