"It starts with one... and it ends with one." Meaning: There really is only one day of recovery - ever. And that's 'today'. This is, I believe, why Teshuvah is one of the things sometimes code-named "Atah" - Today. (V'ata Yisrael, Ma hashem Elokecha Sho'el Me'Imach). It's not that it is to be done now, but that it IS only now. There's no way to do anything for tomorrow, or for yesterday. I can't go to the bathroom extra today so that I will not need to go tomorrow, can I? Same with recovery. There is nothing I can do to "prepare to be sober/clean/whatever tomorrow. Nothing. The only thing I will ever be able to do is be sober/clean today. So to me, the counting and 'adding up' is really silly. It can give a false impression that there is some sort of buildup, like we are going to a 'destination' of recovery. Not so for me. I like what Rebbe Nachman said, "yehudi hu tamid baderech - ein hu yachol lavo l'shum tachlit - A Jew is always on the way - he can never come to any destination". It's not about attaining a milestone. 90 days, a year, ten years... it's all arbitrary, really... The next day will still be just another day, no? Even my old goal of 'dying sober' is arbitrary. To Hashem we don't 'die', at all. It's a fake end. There is no end - that's why suicide is such a stupid solution for problems.... We are always gonna be here, and somehow, we always were. How can there be more than 'today', for us?
Hashem has no 'milestones', does He? It's an endless journey in an intimate relationship and adventure with none other than our Eternal Best Friend.
One day at a time is not a technique or a trick, as in 'just don't act-out for one day, you can do it'. It's much more than that. Like pretty much everything else in the program, it has less to do with 'not acting out' and more to do with an attitude for living life. The only way for me to live is to take my focus off of lusting or not lusting, and onto living. And I completely depend on using the steps, to allow me to do that.