There are several synonyms for the phrase "since god knows when." One possible option is "for ages," which suggests a long period of time that is difficult to pinpoint. Another choice might be "since time immemorial," which has a similar connotation of ancient history or distant memory. Alternatively, one might say "since the dawn of time," which emphasizes the idea of a vast and unfathomable span of existence. Other possibilities include "forever," "eternally," or "since the beginning of time." No matter which synonym one chooses, the underlying sentiment is one of timelessness and depth, suggesting a history that stretches far beyond the horizon.