Beijing is 12 hours ahead of Miami
There is no standard 8-to-6 overlap. Someone joins early or late.
Because Beijing is 12 hours ahead of Miami, the two offices are essentially never open at the same time. If a live call is essential, aim for the very start or very end of a workday in one city and accept it'll be off-hours for the other. Note that Miami follows daylight saving while Beijing stays put, so the times above drift by an hour seasonally.