I don't know, the ADAC site is kind of useless to find out the times of all 3 races.
First race is at 15:40 German time, after the first race, the next race start time is normally in text after the stream of the first race has ended and then the same for the 3rd race time will be published on the livestream link after the 2nd race has finished.
the circuit-sites often have the accurate schedules, as they know the details better. The problem might be that MINI Challenge Germany and FIA GT1 World Champs are quiet heavy numbers compared to the East-German Historic Formula Cup and the East-German Historic Touring Car Cup plus they are not organised by the Masters Weekend organisers