The timezone issue is as much of a problem as you make it. The difference between the east coast and the UK is 5 hours - the difference between East and West coast is 3 hours. Both of those are very roughly in the ballpark of "half a workday overlapping".
That’s a big problem for a 9-5 culture company in the USA.
By that logic they can't even work from east to west coast then.
I am not sure how your clock works but 9-5 work hours will have 5 hours common between the East and the West coast.
It's only a problem if the US and EU sides need to work closely together; most tech companies will have multiple products that can be built independently. IIRC Google Docs is mainly built and maintained in Germany.