Hello , Anna Lochas. Welcome to the SMF. Glad you stopped in and hope you get to liking it here and start BBQing with us.
Please stop in at our RollCall and introduce yourself properly to the rest of the Family .
And add your location to your Profile. Makes it easier to understand your questions.
Now, the Butts. In an Oven, @ 250*F , you should "Braise" the Butts ( water and the addition of root vegies would make a nice sauce). Time for this "could" be as long as 15hrs. However , tracking with a Thermometer is necessary. Time is only an estimate.
If you are going to Pull stage of 200*F Internal Temp. for Pulled Pork , track it with a thermometer that is
reliable and easy to use. A Probe type of therm. can be purchased at Walmart and is a Frugal purchase.
If you want slicing Pork, IMHO , I would go to an Internal Temp. of 180*F , in the deepest part of the Muscle. It should slice off well and be juicy.
Hope this helps and as always . . .