Colour B4 timeframe?

I'm wondering if someone can give me some advice about using Colour B4 before seeing a hairdresser. I bleached my hair about 3 months ago, it got to a yellow blonde with orange streaks. I then used Adore Paprika on it. Then I made a mistake - I tried to use Colour B4 to remove the red so I could use Adore Mocha on it before Christmas, but I did it all wrong and ended up with a mess. So, I bought a chocolate brown box dye, which promptly tinged my hair green. I then went to the hairdresser and asked them to fix it, all they could do was apply a non-peroxide red dye to cancel out the green because the bleach strand test affirmed that my hair would break if exposed to more peroxide. My hair is now really, really dark brown (it looks black) with a red tinge, and I am not a massive fan.

I want to use Colour B4 and then go to the hairdresser and see if they can do an ombre, using my natural colour for the top so I can grow it out, and then lighter at the ends - hopefully light enough that I could put fun bright semi-permanent dyes over it. I'm just confused as to how long I need to leave between Colour B4 treatments and then the appointment?

Thanks guys!