How long do you take Citalopram for and how do you know?

I don't take cit but have do take venlafaxine and mirtazapine and am in the process of weaning off.  I had a very bad protracted withdrawal from coming of Ven a year ago, having been on it for 12 years.  So, I've learned a lot since then. 

I think your approach is a good one, to see it as an aid for the short term and to have a strategy in mind. 

These drugs causes actual physical changes in the brain and the rest of the nervous system.  Start up side effects are caused by the newly created IMBALANCE of neurotransmitters.  The imbalance theory of depression has been debunked.  So, your nervous system's response to this imbalance is to push back and make changes to re-establish the norm.  These drugs block receptors so that serotonin remains in the gap between nerves longer.  So, the body begins to add more receptors to try to bring that level back to normal; it also slows down production of serotonin because there is too much of it in the nerve gap.   This is a simplification but you get the idea. 

The longer you are on a drug and the higher the dose, the more of this remodeling occurs, such that when you come off the drug, there is that much more remodeling in reverse that must occur.  

Doctors have their patients taper off these drugs much too quickly, and the body can't keep up with the drop.  Most "tapers" amount to a cold turkey as far as the nervous system is concerned.  When that drug is removed too quickly, those modifications exagerate the imbalance even further because now too much serotonin is being sucked up with all those additional receptors, and not enough is being produced because that feedback system had been shut down. Big withdrawal effects ensue, and those effects can go on for months, even though the doctor won't recognize WD beyond 6 weeks!  The longer you were on and the higher the dose, the longer it will take to come off.

The withdrawal authorities recommend a 10% per month taper, and that is of the previous dose.  It doesn't matter that you were only on the drug for 6 months; the nervous system seems to be much slower about changing back than it was to adapt to the action of the drug.

So, moral of the story is, don't rush up to a super high dose right off the bat just because the doctor says it is time to updose.  Go by how you feel.  If 10 mg is all you need to feel better, that's all you need, period - why updose?  If you do updose, know that you really will need to taper off as slowly as the 10% method, which is a harm reduction method geared towards keeping people comfortable and functional while tapering.  You may still experience some WD once off but it hopefully won't be as much a nightmare as a cold turkey will cause!