Sorry it took me so long to get here, I have been really busy on this end.
In answer to your questions, first of all, I want to make sure you understand we are talking about a virus here. The cysts don't rupture, they don't fall off... basically they "slough off" or peel away in the water current as the virus runs its course. The tissue of a lympho cyst is mostly comprised of dead/altered skin cells. Just as people shed skin every day, the cysts "shed" in much the same way. It is gradual but to us, appears to shrink like a wart going down.
There is no way to put a time frame on how long the cysts will persist, when the fish can show symptoms, etc. Once the fish has been exposed to the virus they can carry it and/or develop the full blown virus and infection. Think of it along the lines of HIV, which is a virus. Some people are carriers, some get the full blown infection, and some don't get it at all. Some fish are more susceptible to lympho than others.
How do they come into contact with it... its omnipresent. Just as there are algae spores everywhere, in the air, under our fingernails, on our skin, in our hair, etc. so is the lympho virus along with many other virus's and bacterias that are common in aquarium fish. This virus, along with many others, can lay dormant until the conditions are just right for it to actually infect the fish.
How exactly lympho is transported, contracted, and why some fish are more vulnerable to it than others, etc. that is all research that has yet to be done and recorded. What we know about it at present, meaning what the scientific world has discovered and/or shared with the rest of the world where lympho is concerned, is mostly the after effects of a fish exhibiting the cysts, which is the give away that the fish is infected. It would require a micron microscope, among many other things to even begin some of the studies that could be done and lend us more help in dealing with it, identifying it, avoiding it, etc. But, that is expensive and many yrs worth of study by qualified people.
I can offer you some of the things I suspect about it based on my own personal research and study over yrs of dealing with it in freshwater, brackish water, and marine situations, but I cannot offer you the supporting data to back it all up... that data just does not exist yet.
As long as the fish can still function properly, meaning it can still eat, swim, breathe, etc properly... the best thing to do is leave it alone and focus on keeping the fish and its aquarium as healthy as possible. The best way to fight this virus is through strengthening the fish's immune system and lower its stress levels so the immune system can focus attack on the virus.
I have worked with fish that after years in a stable tank situation, no new exposures, suddenly develop the cysts, the cysts last weeks, sometimes longer, then just seem to start shrinking one day and it slowly goes away. Some of those fish never get it again, others will get it repeatedly for no apparent reason. That is why I compared it to the flu in my first post here about it. Trying to pinpoint a given fish's exposure to it would be like a needle in 1000 haystacks. And trying to track exposure time until time the symptoms show up is also not possible because of the many habits of a virus and lack of current study about it.
I'm sorry I can't offer you more exact info to some of your questions. If at some point I learn more I will surely share it with all who need it or desire to learn. I don't think some of these answers will be discovered in my lifetime, if ever.
For your situation, watch your fish closely, be sure its able to eat and function properly, watch for behavior changes as well as physical changes, and focus on that fish's overall health and stress situation. That is the best anyone can do. If the growths become too large or numerous and begin to affect the fish's ability to eat or swim properly, then please let me know and I will refer you to an aquatic vet for the removal of the cysts.
Best of luck to you, let me know if there's anything more I can do to help.