When to go
All months are suitable to photograph from within the Crystal Universe exhibition.
Try visiting in the morning when the museum opens or early evening when it's about to close. It should be less busy then so you can get a clean shot without people around, or at least not wait as long for people to walk out of the frame.
Field tips
You won't need a wide-angle lens for this composition; a normal lens is enough to capture the entire installation's reflection.
You're not allowed to bring a tripod into the exhbition (so don't bring one).
The closer your lens is to the ground, the more optimal your reflection shot will be.
Try changing the style of the lights by swiping different planets and stars from the smart devices within the installation.