Well I see it a bit differently.
My "plan" is to just keep plugging away getting stronger over time until such point as I either get injured or too old to maintain that weight then I'll gradually reduce the weight but continue exercising, MY point being I do not feel like I'll ever "get" to anywhere in particular, rather than I'll be exercising for most of my life because I enjoy it, it makes me feel good, look decent, helps me lift heavy things, work on the car, etc.
For me it's not a process with one goal in mind, it's a life style choice. I've taken time off before, well over a year to let things heal up, persue other interests for a while etc and that will probably happen again, but ultimately I always see myself doing some form of exercise.
Foir you, well you have some kind of look in mind obviously so you will be "done" when you get there and then you need to maintain it.
How long will that take? That's determined by your commitment and determination.
About twice the length from the starting point to about the middle...
EDIT: As for being disillusioned, when I hit a mental wall, I change something. Add weight, new exercise, move exercise around, buy a new gym shirt, take a full week off (you should not overlook the need to do this every now and then anyway).
Then come back refreshed.