depends on how large a pen blank your making in what kind of mold. If your pouring one of the molds that take 9 ounces and makes 3 pen blanks then each pen blank is apx 3 oz.
The biggest thing is the amount being poured. The larger the pour, the less catalyst you use. Too much catalyst and the blank will fracture while curing. Not enough catalyst, it will just take a while to cure.
Not 100% sure I agree here. I'd say the #1 thing is the temperature, with amount of resin being very close. As you get to a larger volume (or more importantly a larger volume/surface area ratio) then the pour size matters more.
When it's 110 even crystal clear alumilite will gel in under 3 min.
Otherwise- it varies with pigments and amount of resin being cast as others have said. Check out my Resin Color Library for a number of empirical examples.