Since Callicates was a 5th century BC philosopher, it would seemly likely she said it in the 5th century BC.
Note that linguistic evidence cannot be used to date the author, because it is very likely the text was changed or emended at some point. For example, Stobaeus, the sole source for the quote, who was writing in the 5th century AD, many hundreds of years later, may have changed or altered the text in some way. Also, Stobaeus may have relied on a different author's rendition of Phyntis, which is even more likely. In this scenario, Phyntis' work may have been related by some compiler in the 4th, 3rd or 2nd century BC who edited the text using language familiar to them, and Stobaeus simply repeated that author's version. In either case, the exact language ultimately received could be different than what Phyntis originally wrote.
Just as one example of this are the "writings" of Aesop, who is one of the earliest Greek authors. The language we have of his is largely believed to be that of later compilers, not his own.