In very hot weather all rhododendrons will look droopy in the heat of the day. That is normal. Unless this is very hot weather you are having, this is not normal. Since it recovers in the evening, it is not dying but is being stressed.

One must be careful in watering a rhododendron. If the soil is not well drained, when the weather gets hot, it will develop root rot. If you don't water a new plant like this it will die. Its root structure has been disturbed and it is having trouble getting enough moisture. Water but don't over water.

It sounds like the plant may have been pot bound before it was planted and the roots are not reaching out and getting water. When planting a potted plant, it is necessary to open up the foot structure so that it will adapt to its new soil.

One thing you can do is, as a first aid measure, place a burlap shade over the plant. This would be a temporary setup until the roots get established. If, in fact, you are getting very hot weather, then I wouldn't get too concerned, but just keep on top of the watering, not too much, just enough.

Do not fertilize. That would stress it more. Wait for it to get established before using any fertilizer and even then don't use much or any at all.

Here is a link that might be useful: How to care for rhododendrons

PS:

If you are concerned about the plant being in the sun, that amount of sun is ideal. They need sunshine in mid summer in order to set flower buds. It sounds like yours may not get winter sun which is also ideal. If it has been very hot, the wilting is normal and just keep up the watering, but not overwatering.

One word of caution, rhododendrons need acidic soild. If the garage has a concrete foundation, then it will leach lime and raise the pH of the soil near the foundation. If it is a new foundation, the effect will be more pronounced. If the rhododendron's leaves turn yellow between green veins, that is chlorosis and you will need to acidify the soil and use a complete fertilizer like Holly-tone. You can acidify the soil with powdered sulfur. Do not use aluminum sulfate, it slowly poisons rhododendrons.

Thanks so much! In fact, it is a new garage foundation. I'll purchase some powdered sulfur (Lowes or garden center?). Should I use the Holly-tone now or wait until it is more established or until it starts showing yellow leaves? I plan to shade it with burlap as we are supposed to get some 100 degree weather this weekend!

Really appreciate the help!

Hold off on the Holly-tone until next year or if you see signs of chlorosis this summer you can use it. Right now, the roots need to get established. I typically use about a tablespoon of sulfur on a small plant. Since rhododendrons have shallow roots, all you can do is sprinkle it on the surface of the soil under the mulch. It is very slow acting and will last a long time. I would say that you could apply a tablespoon of sulfur every year until the leaves stop showing signs of chlorosis. Your first application is to prevent chlorosis. After that wait until symptoms appear.

If you haven't mulched, that is very important in hot weather. It helps keep the roots cool and holds in the moisture.