Depends where they are in terms of sunlight, and whether they're in pots or not - in sun, in small pots, daily, in larger containers, when the surface of the compost is drying out.

One thing about Buzy Lizzies is that they'll let you know if they haven't been watered enough by looking very limp. Luckily, once they're watered, unless they've been left too long, they'll perk right up again.