Once you have decided to go light you want it right now, no waiting, It needs to be done now!
The problem is your hair doesn’t feel the same, to get it to go from one point to another it has to be done in a way that both the condition and integrity of the hair as well as the desired color is achieved. If you lighten it up too fast the tone will change after a week or even a few days. Look at it as transitioning the color during each season to be able to reach your goal by the next season.
It’s not a race, it’s a process.