Re-dying my dark red hair?

My natural hair color is medium-dark brown. For the past 2 years, I've been dying a dark red (Nice & Easy-Dark Spice). Looking at it, you'd think my hair was very dark brown, but in the light you can tell it's red. Now I'm looking to dye it again. This time, I bought Nice & Easy Perfect 10 - Dark Auburn/Cinnamon Red Hot. It is a shade or two lighter than my current color. It easier to tell it's red in any type of light, which is what I'm pretty much going for. I want it to be obvious that I have red hair, but I don't want flaming red or anything, if that makes sense.

I just dyed my hair with the Dark Spice about 2 weeks ago. My question is, how long should I wait before trying this Perfect 10 shade? A few people suggested waiting a few months, but I purposely want to do it now so my hair is all one color. If I wait, the top half of my hair will be dark brown and the bottom half will be dark red, so when I dye it it will be two different colors and I don't want that.

Any stylists out there who can help me out? Or has anyone done this type of dye job before?

Thanks!