Night time is my favorite time to drive top down as well. Though I love convertibles and always drive top down in my MINI, I am not a big fan of being out in the direct sun on warm days especially if it is city driving with all the stops.
I am happiest just after sunset when the moon and stars are coming out, the city lights are coming on, and the heated seats are keeping me nice and toasty. It is heaven on the highway.
I am always amazed at how few people actually use their convertibles with the top down. I think there ought to be a law against it.
By the way, yesterday was my 8th wedding anniversary. What did my wife and I do to celebrate? We went for a nice long drive in the MINI, top down of course.