Answer: Hydrangeas sometimes wilt in the afternoons due to heat stress, then recover later in the evening when the temperatures cool down again. I suspect this is what you are seeing, especially since your plant is newly planted and has not yet become fully rooted and established. Make sure the soil is evenly moist like a wrung out sponge, not sopping wet/saturated and not dried out. Using a layer of organic mulch can also help keep the soil cool and moist.
Hydrangeas need some direct sun in order to bloom, but do not do well in all day sun or sun all afternoon. Hydrangeas do best in a location with direct morning sun or bright dappled light all day. They also need protection from winter winds. Based on your description, your plant may not be in enough sun to assure good bloom performance. I would suggest you check with your local professional nursery staff if your plant continues to look dry.
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