As I'm working on legendary armor in WvW, skirmish tickets are one of my key goals. Generally I'll play once in the morning, then again in the evening, staying long enough each time to get two of the skirmish ticket chests. Sometimes it seems like I get two chests fairly quickly, in an hour or less. Other times it seems to take longer, from an hour and a half to two hours. What determines when we get those chests - specific time intervals, getting a set number of pips or something else entirely?