It’s dependent on the amount of calories consumed vs calories used, and not so much on the time of day. Metabolism is a continuous process that’s practically always in motion so weight gain/loss is only noticeable with cumulative effects. If someone eats more calories than their body needs for the day, those excess calories are stored in fat cells, eventually causing noticeable fat accumulation. On the flip side, if the person needs more calories than they’ve eaten, the fat cells are burned as the “reserve” fuel, causing weight loss.