Does IRay automatically handle SSS or do I have to turn it one like in Poser? 

Depends on the texture/material you have applied to the character. If you use a material built for Iray then you shouldn't need to do anything (unless you want to tweak). If it's other materials you will need to set it up and use appropriate values. But there are a couple of default materials included with 4.8 that will get you most of the way so all you need to do is tweak the settings. You can also set up your figure with a non-Iray material, ctrl-click an Iray skin material to apply it, choose ignore, and then you get those Iray settings on your current material. "How long do I have to let an IRay render run to get smooth skin?  No speckles."

Speckles?? Do you mean fireflies?

It's impossible to answer. How long is a piece of string? How big is a hole?
It depends on how quick your CPU is, what you have in your scene, what you are doing in that scene in regards to lights, shadows, SSS, caustics etc etc. You could try messing around withe the render settings, change the quality, max samples, make sure the firefly filter is enabled. But if most of those are increased, then so is render time.