Even if we’ve been a conscious, deliberate sinner or have repeatedly faced failure and disappointment, the moment we decide to try again, the Atonement of Christ can help us. And we need to remember that it is not the Holy Ghost that tells us we’re so far gone that we might as well give up.
Elder Dale G. Renlund, "Latter-day Saints Keep on Trying", General Conference, April 2015
We don't need to "prove" that we are trying to change by going some time putting work in before we can rely on the Atonement of Christ.
He steps in as soon as we want to change. Even before we actually put girth some effort and only express a desire to be better, He does immediately step in to help.
Immediately. Not tomorrow. Not when He has a second. Immediately. Right that very instance.