As far as I know GTB is "Greece Turkey Belarus", which is GMT+02:00. I believe that is the actual time zone in Bucharest. Add another hour for daylight time. The event is supposed to start at 10 AM BST, British Summer Time, which in turn is GMT+1:00. Thus it should start at high noon in Bucharest, just as always.
GamePress
Did community day hours change?
I cannot figure out what GTB 12 PM - 3 PM Daylight Time would be for Bucharest, the only convertor I found just said it would be 10 AM here, I hope that's not the case, it would take me too long to get to the park I plan to go to on CD so I'd miss out on a whole hour then.
Normally CD would take place at exactly 12 pm until 3 pm here too.