It is 'ok'. Not dying but, rather, wilting due to the sudden heat that the plant is not used to getting... remember, it was coddled/protected so much at the plant nursery and wholesaler. In their first summer or in their first few summers, they do this but should be able to recover on their own overnight, provided that the soil is moist.

Make sure that the pot gets, at most, only morning sun until 11am or so. Then water early in the mornings when hot or when windy. And consider more watering (twice a day) if conditions warrant it (by that, I mean, that the soil dries out again; do not water if the soil is already moist/wet and the plant starts to wllt).

The pot appears to be made of plastic and those pots can heat up during the day and make the roots "uncomfortable". So a more shadier location will help.

So basically, provide more shade and more water. You can go down to as few a a couple of hours of sun but no afternoon sun, no evening sun and no windy locations that may dry it out.

If blooms brown out, you can deadhead them.

Just remember that you want the soil to be moist, but not totally saturated/soggy. If it's too wet, the roots will rot, so keep a close eye on the water, give it less sun, and check the soil to see how it's doing. If you want to keep it in a container long-term, you might want to visit the container forum for suggestions on soils that will hold up or do some reading on soil mixes for container growing.

Thank you. I am keeping the plant in the shade almost whole the day. Do you think it is OK? The pot is ceramic and I will keep it in it for some time. Shall I wait with watering the plant until the top of the soil is a bit dry on the top?

One thing to consider also may be that pot may be a little too small. Can't totally tell from the angle of the picture. It could also still be in a bit of shock from being planted.

Here's a thought.. Hydrangeas, unless this is one of those supermarket indoor plants, should be in the ground and not in a pot. Its terribly hard for plants to thrive in pots because of the circumstances you have just described. For now, keep the roots alive by watering it from below.. Keep the pot on a tray and fill that tray with water. When fall comes along and the plant goes into dormancy, put it in the ground and mulch it well. If all goes well, come spring it will sprout new leaves.

I'm just assuming you are in an area that experiences winter.. If you happen to be in warm california or florida, then lets use a different approach..