I've found that the time it takes to house-train does vary from dog to dog.
Our first lab Stella was more or less clean when we got her as a rescue at about 9 months; Stanley took at least 6-7 months before I could fully trust him & all though his life he wasn't too bothered about messing indoors if he got caught short!!
Sidney was clean practically from day one;however in those days his breeder & I trained them first on newspaper so the whole process took a lot longer than it needed to.
Spike was almost totally clean at 14 weeks & now would rather slit his own throat than mess indoors & Domino being extremely quick & intelligent took very little time to grasp what was required!!
When Spike & Domino were puppies we took them outside at very frequent intervals & I would set the alarm for 2.30a.m. & go outside with them. I found by doing that we didn't get any accidents during the night.
Now they are both adult the longest I would expect them to hang on would be 4 hours; although Spike sometimes doesn't bother to go first thing in the morning- he likes to make sure he gets his breakfast first!!