Going back to the OP question, testing a UV inhibitor will take a longer time than long, long, long, long. I prefer the complete package so to speak than the two-part system. However, I don't think all UV inhibitors are the same. They can look the same, but I've seen two powdered versions that look a pale yellow do different things.
Testing it ... I'd say put it in your candle and stick the candle in the window to see how long it takes to alter itself. On the short end of say two weeks, I've seen colors change drastically ... is that because the UV failed or because the FO decided to make it's change or because of its construction change all the color from black, green, yellow, pink, orange etc. to brown. I have one fragrance that got sent to the incense only pile because it wipes out the color no matter what I do to it ... I just am not a brown patchouli fan.
Now I would say if a UV can't make it to two weeks, it's worthless and try someone else.
None of that is going to help you though unless you're able to get orders from somewhere else to India.
For me, the UV is the last thing in the world I will test or check, but it will become the first if I start noticing my candles make huge and obvious changes when there should be none. Hope that make sense.