yes it is true, but we will all define "peak" differently. As time goes by the buds get riper, meaning they increase their canabinoid resin. There are two main canabinoids, CBD and CBN, these are molecules that bind to the same receptors in ur brain as THC, which is produced during curing and ripening as the CBD and CBN break down. CBD and CBN do different things; one provides the heady high, one is the couch lock high. So at some point in the grow, you will have ideal levels of both for your favorite kind of stone. When? Almost no way to tell, but when the trichs are turning amber that is an indication of CBN production. When half are amber you have a good mix of both chemicals which is when most people harvest providing what most would say is the best effect. Some harvest early for the head rush stone and some harvest late for the sleepy stone. It all depends on what ur wanting from the weed. However, it won't start getting less POTENT until u are far far past the best time lol, and no matter what chems are in the plant at harvest, a good cure is what finishes converting those canabinoids to THC which we all seem to enjoy more.
so basically don't WORRY about it, but yes, there is a best time to harvest. the window is large though, days long, so it's hard to miss and impossible to "fuck up".