As for the hidden classes, they are probably intermediate at level advancement, perhaps at 30 and 70, who knows. I do not know what it means for the class to be hidden, and if it's hidden why they list it.
The hidden jobs are at any time between 2nd and 3rd advancement but you have to find the npc and finish the quest which is usually hard.(P.S. this is just my theory I could be wrong or I could be right.)
Taiwan Dragonica is going into CBT this month, company's gameflier. (not the same as China Dragonica)
Also, the 2nd job advancement is at lvl 40.
Just FYI and to add on to the FAQ.