Pay very close attention to the helicopter tour times announced on the companies web site. All tours are hand picked for sightseeing at the best time of the day.
Early morning flights to mid day should be suited for all as its the brightest time of the day; allowing you to see at the furthest distance well making perfect photography conditions.
Think of the summer time as the longest days so all applies later into the afternoon and early evening.
So, if you can, book a helicopter ride for mid-morning to mid-day to allow for the brightest time, and that's if the weather doesn't spoil things.