I'd say start from day one. Even from conception. All of the advice and encouragement is a great part of the thread, but probably the most useful part of a build thread is being able to look back and see exactly what you did and when you did it. You actually wind up with a chronological record of the evolution of your tank. How cool is that?! Imagine looking back after years to remind yourself how long you used this before you switched to that. Why you will never do THAT again. And exactly how long this piece of equipment lasted before it had to be replaced.
Admittedly, I'm guilty of letting my build thread go woefully out of date. I keep telling myself I'm going to update it, but the longer it goes, the harder it is to do. :(
