Some people do season the WSM prior to its first use, but it's not necessary. It's ready to smoke as soon as it's assembled. However, it will probably run hot the first few times it's used.
There are charts, scales, sacred symbols and shamans aplenty on the internet, man, but those are all rough guides. Given that, the rule of thumb for pork butt is 1.5 hours per pound at 225-240. But the true measure of a butt being done is probe tenderness. It's done with a temperature probe goes in with no resistance.
You can use the 1.5 hour per pound to help plan when to be done, though. So, if you have an 8 pound butt and figure 12 hours, you can put that sucker in at 6 a.m. for a planned 6 p.m. dinner.
If it finishes early, you can wrap it in foil and a towel and put it in a cooler. You can hold meat in a cooler for a couple of hours (I've gone up to 5) with no problems.
You can Google cook times for various meats at various temps.