There is no formula to follow, you must water as needed. Temperature, wind, size of the pot in relationship to size of the plant it is holding will all come into play.

When I water containers I fill to the brim until water is running freely from the drainage holes in the bottom. Depending on what has been used for potting medium, if allowed to completely dry out some can be very hard to rewet, water may go around the rootball and out the holes while the rootball stays dry. If that has happened, you may need to submerge the pot in a larger container of water, hold it down if necessary until bubbles stop rising, then begin watering as needed again.

And drought tolerant plants are not drought tolerant until fully established in their permanent site. That can mean more water the first year or more until the plant has established a more mature, functional root system in the ground - literally nothing newly planted is drought tolerant.

So, how do I know if they need more water or if I already over-water them?

Poke your fingers down into the pot...feel. Pick up the pot, how light is it? Water, then check again so you have an idea what a fully watered pot feels like. When you do water, don't just give them a little, give them a slow steady stream until water is coming from the pots drainage holes.

If your plants are going limp a couple of days after watering, you are not overwatering. Disregard the suggestion on the plant tag for the Indian Hawthorne, it's for a hawthorne once established in the ground, not now in an unnatural environment (its pot). Yours won't be established until a year or so after you have planted it.

The soil material in pots from the store also may not hold as much water. For example, when you water, the water just flows right through, and by next day, the plants are wilting again.

Since they do have some problem retaining water, you can also keep them in light shade or morning/early afternoon sun for now until you establish the areas where they are going to be planted.

You might not be able to get the soil ready for them as fast as you can get ready a hole that you dug for them. So if you focus on the hole that you are digging, and amend it properly, that will already help the plant, in case it is taking longer to fix up large quantities of your soil.