Well, you and I live in very hot summer locations so to answer your question, IN THE SUMMER, I would not wait for it to dry out before watering.
Instead, I would use the finger method (or you can also try moisture meters although I do not like them because they do not appear to be very accurate) and develop a feel for what "almost dry soil" feels like. Then water when the soil feels almost dry. You should use the finger method in the mornings, at about the same time (6-8am perhaps), so you can compare how the soil feels from one day to the other.
In the Spring and in the Fall, when it rains here, I can be more restrictive with the water. The reason for limiting the waterings is to prevent root rot in plants that sit in wet soil IN THE GROUND. The chances of that happening where you and I live in the summer, and on a potted plant, is usually negligible so again, in the summer, you can water again as a precaution if the soil feels "almost dry". If not sure, in the summer when temps are over 95 or so, water. As long as the exit holes in the pots are not clogged in the summer, the chances of getting root rot in pots are low.
Signs of trouble: the leaves begin to brown out from the edges inwards (needs water). Or the blooms brown out first without going thru their normal plethora of color changes first (say from pink/blue to a mix of greens and other shades of pinks, ending at some point in brown): needs water and in general, it is too hot and gets too much sun. Leaves wilting 24/7 and does not recover at night after you water it...indicates root rot.
Evening sun can also be bad so monitor the plant. Our normal summer temperatures have very high temps at night, like from 5pm (highest temp) until sun down (9pm-ish) when temps come down to 100. So also consider doing what some people also do, which is to use pots for the plants and then enclose a pot within another pot (say, use a squarish wooden and bigger pot to enclose a wide pot where the plant resides). That way, the plant's pot does not receive the hot direct sun and the sun does not start to bake/harm the roots.