They don't "have" to be in water at all. It's about 100 here all week and from seedlings to my big ass Spiderman are not water. I do have a tray with a few seedlings in water. If it looks tired (limp foliage) even after regular watering then might be a good time to dunk or reduce sun exposure. In ground BC is used to regular temps in the high 90s without flinching, in a pot you should be a bit more cautious.