Thanks for the comments...

actually there aren't almost any settings to tweak since Maxwell is a unbiased renderer. That's one of the good things, it's easy to use and get realistic renders without going through tons of settings. Sure it's possible to get a photorealistic render with MR, but you have to be a God of MR to get it as good as this. I think my previous MR renders sucks compared to the one I render in Maxwell.

Usually a couple of hours gives a nice render, but it depends of what you're rendering, a whole room with light to bounce around in takes much longer time apparently.