Dr. Tim's is nitrifying bacteria needed to establish your bio filter and thus to "naturally" neutralize ammonia and nitrites. It works differently from Prime, which de-toxifies by chemically changing the ammonia and nitrite, but not removing it.
Dr. Tim is the man who created biospira, a product that was decidedly NOT snake oil. Biospira is now Tetra Safe Start (and I can't attest to its efficacy.) But I have used Dr. Tim's several times and find that is does work -- although not 100 percent of the time. Out of several bottles I used over the past six months, I believe one was "dead." In the other cases, one bottle handled my nitrite problem overnight.
I always keep it on hand, myself, for good measure just in case of emergencies.
Although I agree with one of the previous posters -- with a three gallon tank, I'd probably just be doing water changes at this point to keep ammonia down.