Not an expert, but based on my experience, the only things that you need to be concerned with are sunburn, heat stroke, or dehydration. I trim basically year 'round, with discretion, and have never encountered any problems. With bushes and hedges, we generally try to remove any dead sections during the winter, just because it's easier to see what you are doing with less foliage, then shape them as much as possible in late winter/early spring, so that the new growth fills in evenly. The only thing that you will find in trimming this time of year, depending on the type of bushes and how aggressive you are, is that they may not fill back in until next spring. Otherwise, put on your sun screen, wear a hat with a brim, keep the mosquito spray and water handy, and have fun.
I'm "Coach Dave", Garden Expert for The Home Depot and I have plenty of experience with trimming. The answer is "It is better to do lawn work such as trimming in the daylight". The reasons are: when you finish:mowing,trimming,fertilizing, and planting you should always water. You should never water at night because this will cause fungus and create a problem. The other reason for early morning yard work is visibility, it's safer when you can see.
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