A few months during brumation. When awake but in hyper mode (right after brumation) like right now, usually a few days and even then he doesn't eat much. One roach last time I offered them. A few pieces of squash etc. During normal activity level time he eats salad daily and sometimes wants two salads.
My beardie managed to go into brumation at 6 months old and didn’t eat for 6 weeks, the only reason it wasn’t longer was cause I had to get her up and eating again due to her weight dropping.
I dont know about adult dragons but I’m fairly certain they can go months at a time while in brumation.