Humm.. I actually thought about this, and posting at night does has its advantages, especially if you have a comic that's character driven or has angst in it...
This hasn't been proved scientifically yet(i don't think), but some people (including me) tend to be much more emotional at night, and that's when you can really make your readers cry
Then again, Tapas is used by people all around the world so posting at night means updating during the day for a lot of people.
So i guess what I'm saying is, go for it since it doesn't matter anyway