From my recollection of my developmental psych courses, the studies on this subject generally control for "time available" by including cohorts of adults in full-time immersion programs, or even adults who move permanently to a new country. The results have always consistently shown that even with dedicated study and full time immersion, adults will never reach the same level of linguistic fluency as would a child within the critical period (generally < 11 years old) because they're incapable of acquiring the phonemes of a new language to the same degree as a child, due to fundamental limits of neuroplasticity in the regions of the brain responsible for language acquisition.

So yes, obviously if you don't have time as an adult to learn a language, you won't learn it as well as if you can dedicate the rest of your life to it. But the point of the results of "critical period" studies is that even if you dedicate the rest of your life to it, you'll still be at a disadvantage compared to a child, when it comes to attaining perfect phonetic and linguistic fluency.