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Probably 5 or 6pm
 
Yes, but the US gets the update first. Apple is based out of Cupertino, California, USA.

Most software companies would time a large release like this to be during their business day. That way, everyone is on-site at their desks, and if something bad/unexpected happened it could be fixed a lot quicker than paging engineers and waking managers up.

Apple usually starts releasing stuff at the beginning of the work day in California, and they're 8 hours behind us in the UK (i.e., 9am there is 5pm here).
 
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