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Either or. Personally I like to apply the rub about an hour before I throw them on. At times, depending on the amount of salt in your rub, they can get a bit of a hammy taste (of course it is pork) if rubbed overnight and the salt also draws some of the moisture out of the meat. But with that being said, I have done them both ways and they always turn out great.
Spares? Baby backs? Are you planning on the 3-2-1 for spares or 2-2-1 for baby backs? What are you cooking on?
Depending on the temp your smoking at and the tenderness your looking for, you might not need the full 2 hours in the foil. I would start checking them around 1 hour and 15 minutes in the foil. Toothpick test in the meat, if it slides in easily, they are done, a bit of resistance, let them go a bit longer. Good luck with your smoke!