Bucharest is 6 hours behind Beijing
Best overlap: 2:00 PM to 6:00 PM in Beijing is 8:00 AM to 12:00 PM in Bucharest.
Target 2:00 PM to 6:00 PM in Beijing, which lands at 8:00 AM to 12:00 PM for the Bucharest side. A 4-hour overlap gives you a workable daily window; aim for earlier in it to avoid clipping the end of someone's day. For part of the year the maths changes: Bucharest observes daylight saving, Beijing does not, shifting the overlap by an hour.