I did it a million times. Whether it was the first day of the month, the first day of the week or, the big one, the first day of the year. I was convinced THAT was my day!
However, you will never suddenly wake up one day and change everything about your life that needs changing and never look back. So instead, stop waiting the first day of something and realize that every day is the first day! Every single day is an opportunity to make a little, tiny, itty bitty change that will snowball one day into a new life.
So, it's April 1st. Go ahead, make a change. But decide it's going to be a small, controllable change that you can live with for the rest of your life.