You can switch over now, or not even use the mineral oil at all if you plan to use synthetic for the long term, although the Castrol 2T is good dino oil. I use full synthetic from the first tank, 32:1 for the first gallon then 40-50:1 there after. There are no good reasons to use a different oil for breakin than we want to use for the rest of the life of our little toy airplane engines.