If your body feels up to the challenge -- go for it. There's nothing wrong with two-a-days occasionally. It might provide a good "shock" to your system.
I think you'd be better to do legs in the morning though -- otherwise your back will be pre-exhausted from doing back in the morning and you won't be able to squat as well.
If I was to do this, I'd probably try to do my morning workout heavy and my evening workout a little bit lighter (i.e. all cables/machines). If you try to go balls-out on everything, you might dig a little to deep into the recovery reserves. I'd also make sure I had a day or two off after this workout.
Personally, I'd probably just make it up on an off day. Are you on cycle right now? If so, that counts in your favor.
Bottom line -- listen to your body. See if you feel up to it for the evening session. If you do, go for it -- it could be a lot of fun. But if you don't, it's better to error on the side of rest than overtraining.
IMHO