Never use GetDate() when comparing date timesoffsets, use SYSDATETIMEOFFSET()
-- my current uk time is 2014-01-09 10:43:00 +0
DECLARE @userLocalTimeChina datetimeoffset(4) = '2014-01-09 18:43:00 +08:00';
DECLARE @userLocalTimeLasVagas datetimeoffset(4) = '2014-01-09 02:43:00