Our regular fight nights are Tuesday, Thursday, Sunday 9PM - 1AM (or later) Eastern US Times. This week we had a few games on Monday and Wednesday nights as well.
There is a bracket-history project that gives detailed information about this and the Reckoning forums are fairly active:
Generally speaking Eastern US is either -5 our -4 hours "behind" UTC/GMT, depending on daylight savings time (also known as "Summer" time in Europe).
Germany is +1 or +2 "ahead" of UTC/GMT, depending on daylight savings time.
Basically Germany is usually 6 hours ahead of Eastern US. Adoption of daylight/summer time isn't synchronized so twice a year you may have a week or so when it's only 5 hours but that's just twice a year.
So, our
9PM - 2AM Eastern US Time typically games would work out to
3AM - 8AM German Time (Central Europe)
Wouldn't you have to make a whole new US account to play on US realms? Also, the Reckoning realm is hosted by the Blizzard datacenter in Los Angeles, CA on the West Coast of the US. While this isn't a problem for time zones your latency might be quite bad.
Yeah, forgot this >.< I would transfer if i could play with my EU Account, but i can't pay a second acc just to transfer my Char and i don't even think that i'm able to transfer from EU to US account.
Now i have to hope that cross battlegroups will come with cata. The german bg "Blutdurst" is the most active twink bg, so there could be an active twink community again with cata.