I used to absolutely not bother about the accuracy of my quartz watches, simply assuming that they are all super-accurate, adjusting them once in a blue moon when switching timezones and then a little more frequently since the advent of daylight saving time (I hate that BTW).
But then I started collecting watches, including quartz, including digital quartz... And when I adjust a bunch of them, just after a BST/GMT switch, I can not help but notice differences big enough to bother me.
So, given the duration of 6 months, i.e. the duration of a period of daylight saving time or its dual (nightlife wasting time?), what would you consider an acceptable deviation, and what is still an excellent deviation - for a quartz?