Should I set a time limit and if I am unable to quit drinking by.....
Sure, how about now!
It sounds like you are open to going to AA, so tomorrow go to an AA meeting. Tell your story like you did in your post and ask for some help. It dosen't sound like you can quit by yourself, setting a time limit isn't going to do anything. Even if you can "white knuckle" it somehow until you hit your time limit, it dosen't sound like you are going to be able to stay sober.