There are two weeks of school left but I want to color my hair?

I have about twelve days of school left (both full days and half days--the half days being exam days) and so I really want to dye my hair before school is out. I have dyed my hair before; the last time I dyed it was around the end of February/beginning of March when I got in trouble for showing school spirit. The color that I dyed half of my head was red. Red--like the actual color red. I naturally have dark brown hair so the color "wouldn't show" but it did... it was vibrant but at the same time, it bright like natural blondes' would be.

Anyway! With twelve days left, do you guys think it would be safe to dye my hair the same red or should I wait a bit longer? I don't plan to do the WHOLE head--I'm thinking that I should dye the longer strands (I have an undercut so only the top of my head can be pulled into a ponytail).. When my hair is down, it would be ideally be harder to see the red and when I have my hair up, the red should dominate the top of my head.