I'd been watching the forecast all week and getting progressively more depressed about not purchasing flexible tickets. The rain started before we got there but we were prepared; layered up, waterproofs and good walking shoes (with a change of shoes in the car).
I booked for 4:30pm, I really wanted to catch the last of twilight before the sky turns black. I think this gives the best photos and wasn't disappointed. You're guided through the gardens passing various sections with a nice mix of stunning lit trees and objects.
Despite the rain we thoroughly enjoyed it and it didn't slow down my photo taking, although I think it did slow my phone down and I quickly started to run out of battery!