Dealing with Prestige Classes

My group is currently set up to play PFRPG in the Dragonlance setting. We've found some resources online converting DL to Pathfinder, but my question has to do with Prestige Classes as a whole.

I'm playing a Wizard and going into the Wizard of High Sorcery prestige class from DL. For Wizards, in the PF core Rulebook, if I am choosing Conjuration as my focus school, one of the abilities states: " At 20th level, you can change the duration of all summon monster spells to permanent". Is this 20th Wizard level or 20th level period since the Prestige class is just an addition to the base class?

The converted prestige class can be found here: http://www.guilesworld.com/role-playing-games-stuff/dragonlance/wizard-of-h igh-sorcery.html

20th level Wizard. All school benefits, sorcerer bloodline abilities, cavalier orders, and... well... pretty much every other class ability is based on class level, not character level. Adding to your spellcasting ability doesn't change that, any more than a class which has levels stack for purpose of fighter feats would increase Weapon Training. Exceptions to this rule are usually explicitly pointed out as such.

Thanks! :)