The pattern is a burst of roughly five or six flashes about half a second apart, followed by a synchronised dark interval of several seconds. Neighbouring males adjust their timing to those around them, and synchrony spreads locally through a hillside rather than being conducted from any central point.
The leading explanation for the pause is signal clarity. In a dense display, a female's answering flash would be lost in the general glare, and the shared dark window gives her reply somewhere to be seen. Males then orient to the answer during the gap.
The display season is short, usually a couple of weeks in late May or June depending on soil temperature and rainfall, which is why Great Smoky Mountains National Park runs a lottery for viewing access. Predicting the peak in advance remains imprecise, and the announced dates shift with the weather each year.