How and when do I recolor over bleached blonde hair to my original dark blonde. I need to do it on my own.

Basically, it's a re-dye job. You can do it whenever. There's no advantage or disadvantage in waiting.

One thing you need to realize is that even with dark blonde hair, the natural pigment was bleached out and must be replaced. Most hair dyes are formulated with the assumption that they will be used on medium brown hair. When you lighten medium brown hair with hydrogen peroxide, you generate a lot of red. The dye formulators assume that there will be a lot of red present, so they add green to counteract it. In your case, red won't be present, so you'll have to add some in. There are two ways to do that: 1) pre-dye the hair reddish, 2) mix a reddish tint with the tint you're going to use. In either case, you need to do strand tests to make sure you have enough red -- but not too much.

Good luck!