In my experience, the Gaba boost effect from taking clonazepam, continues to have an effect for up to 6 months, and then you may have to switch to another kind of booster (there are many, like brown rice, some amino acids and other things). Another important thing is that for us, low doses are effective but high doses are not. After about 6 months, I found the effect tailed off - apparently the brain gets lazy (habituates) and decides "Since I have a reliable source of GABA coming in for free, why go to the bother of making it myself?" So the total level in the brain actually falls at that point, even though you are taking the same thing in the same amount. A mistake people make at this point is to take more to try and get the effect back - that doesn't work at all. If you want to continue with clonazepam, you have to come off clonazepam for a while and after about two months, you can restart it with the same dramatic effect.
A book I found immensely useful was "The Edge Effect" by Eric Braverman - he provides very useful tests in it that you can do to assess the relative levels of all four transmitters (GABA, dopamine, acetylcholine and serotonin) so that you can measure which are dominant and which are deficient at any time - and he provides some comprehensive information on how to raise the deficiency levels by various means (amino acids, herbs, foods, vitamins, drugs like Gabapentin) and in what amounts to use the various neurotransmitter boosters. There is a wealth of information in it, though if it has a weakness, I think his knowledge of different amino acids and their uses for raising GABA is not as extensive as some other writers.
Clonazepam's advantage from my experience is that it works faster than any other substance (within half an hour). I use it spasmodically rather than everyday now, and there are no more habituation effects. Braverman sells a special GABA boost compound called BeCalm though I haven't tried it (unfortunately importing GABA without prescription is illegal in New Zealand). It is available in the USA and I would be interested in feedback from anyone who has used it. There are a lot of studies on GABA deficiency in autism and I wish this knowledge was more widely known; the deficiency seems to be innate in most people on the spectrum, and some scientists have even theorised that autism is, essentially, a GABA deficiency state. Everyone I know who has trialled raising their levels has noted the improvement to their anxiety, in each case the effect was fast and dramatic (as it was for me in the first few months). It made a tremendous difference by boosting my focus and motivation too. It may not work for everyone (we are all individuals) though it certainly made a huge difference to me.