For me, it is not a time limit.
I say my dog is housebroken when he does not have any accidents in the house and I no longer have to anticipate when he needs to go. When he will come get me when he needs to go, won't stop telling me he needs to go if I misunderstand, and will hold it while I untangle myself from whatever I'm doing to go take him out. Anything less is to me not truly housebroken, it's me getting the jump on him before he has an accident.
My current dog was house trained at about 8 mos. old. My last dog never quite made it there - either you came the first time he stared at you slightly more intently than his usual stare, or there was a mess on the floor. But, by most people's definitions he was house trained. He never had an accident if kept on a schedule.