Looking at the Material Safety Data Sheets, it appears that the only difference between SC I and II is the proportion of the solvents. And, as Bob says, they both work fine on metal, the only difference is that the SC II is much less likely to damage common plastics. They can both be baked on, although that probably wouldn't be a good idea on camera lenses.
And, yes, they take a LONG time to fully dry. I usually allow a week, and they should be protected from dust in the air, as much as possible, while drying.