But you are making assumptions which are not really true anywhere. Working hours I Spain and Germany are already white different. Main reason is of course that they share the same time zone by law, but are not geographically in the same time zone. But there are some additional differences in culture which extend this effect.
Sure, but that still means you are not reaching someone by phone at work during 4 hours of you previously mentioned 8-17 Windows.
As someone currently working from Ireland with my usual office in Germany (laptop still configured this way) with a Team from India and DST ending next week, I would prefer to drop the calculations and just remember when each colleague approximately comes online. That is not the same for each colleague and day anyways.
xkcd #2846: Daylight Saving Choice ( imgs.xkcd.com )
xkcd.com/2846...