A fronted adverbial phrase

Meanwhile, some Brahmins had little interest in ritual sacrifices and more interest in probing relations between self and the universe. They were interested in attaining religious bliss, and perhaps as early as the 700s BCE their writings were collected into what would be called the Upanishads, a collection of as many as two hundred books that were to be written across centuries.
[The Upanishads http://www.fsmitha.com/h1/ch05b-ind.htm]

I'd like to know if "perhaps as early as the 700s BCE" is a fronted adverbial phrase.
Thank you in advance for your help.