Just go early enough that your tour is finished before sunset. After the tour completes you can roam the gardens and wait for that perfect shot. Plus, if you try to get that perfect shot during your tour you will be fighting the crowd, once it's complete you can find a better shot more easily. (the tour is usually one hour depending on which tour you do)
Weather in that area can be unpredictable, fog can set, overcast, etc. Its best to check the current week forecast, much more in advance wouldn't be accurate in that region.
I agree with others that you should go earlier that you are able to preplan outside areas to take a really great sunset photos. The photos near the "golden figure" fountain has a gorgeous view with natural outline of the water and land.
Not easy to predict a month and a half in advance
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