I'm just looking for rules I can look for in the book or written by someone who developed the game. That's it.
There are no official rulings, other than the Corebooks and Errata. There are some people who were involved in various roles with development who have made unofficial posts. Namikaze lists them. What you are searching for does not exist.
However, there are no costs available for Initiation during Character Generation. Those references I can find point towards it being post character generation, but unclearly enough that a GM call could be made either way to suit their table. If creating a character you wanted to play outside that table, at a Missions event, take the Missions rule, which is effectively House Rules for Missions. I don't plan to play at that, so I look at those only to decide my own House Rules when I start GMing.
Things I found in the rulebook that point to post Character Gen :
METATYPE & SPECIAL ATTRIBUTES Core pg 66 : "With Exceptional Attribute, you can end up with a maximum Magic or Resonance rating of 7 when
starting the game (
before initiation or submersion)."
I take that to mean starting the game happens before initiation.
MAGIC Core pg 278 : "Magic has a
starting value from 1 to 6 (or 7 with the Exceptional Attribute quality), but you don’t have to
settle for that limit forever. You can go through a process called
Initiation (p. 324) that can enhance your abilities."
I take that to mean you are limited to 6 (or 7) at Character generation (starting value), but you can later Initiate.
POWER POINTS, Core pg 278/9 : "At
character creation, adepts receive Power Points equal to their Magic attribute, while mystic adepts have to buy Power Points with Karma.
Subsequently, Power Points can come in two ways. If you’re an adept, you get a free Power Point whenever you increase your Magic attribute (though this doesn’t apply to mystic adepts), and you can gain a Power Point through
Initiation (p. 324) instead of gaining a metamagic"
I take that to mean you have Power Points equal to Magic attribute at Character generation, but can later initiate.
There is a Karma cost for Initiation in Character Advancement (pg 107), but it is greater than the maximum 7 you can spend in this area during Character Generation (pg 98).
I state again, though, there is nothing that states it may not be taken during Character Generation, and nothing that says it may. Your GM's ruling, whatever it is, is final.