The amount of cycles used seem to vary a great deal from what I've seen. Some places report the number of cycles they used. Some do not. They do seem to be higher than 30 and I've seen as high as 45.
As to the difference. I pretty much go off of what the guy who invented the PCR test stated.
Whether it is insignificant or not would also depend on the sample size.
Regardless it is relevant to the scientific method to be consistent. Opinion on insignificance is not part of the scientific method. It is something that corrupts it.
I did a quick search...
Here is one article.
They recommend up to 40 there... Though there is no STANDARD which is a big part of the problem.
CT is the number of cycles.
It is a rabbit hole. If you search on your own you'll likely find some useful info I don't know about.
Here is an interesting article:
Coronavirus: The Truth about PCR Test Kit from the Inventor and Other Experts – Video