At around six months you may start feeding twice a day for convenience but because your dog is a mixed large breed dog I would recommend sticking with a 3 - 4 times a day feeding schedule if possible to minimize the risk of gastric dilatation volvulus. (cesarsway.com)
Are Dogs Fed a Kibble - Based Diet More Likely to Experience an Episode of Gastric Dilatation Volvulus Than Dogs Fed an Alternative Diet? (veterinaryevidence.org)
Small size of food particles and age as risk factors for gastric dilatation volvulus in Great Danes. (breedingbetterdogs.com)