Hair dye help please!!!?

I have this hair dye i want to use, its colorsilk by revlon in burgundy and i want to test it out on a small section of hair to see what it looks like, but im afraid that if i make the dye it wont last for 4 days, and i need it to last that long, so my question is how long does hair dye work for after you mix the 2 solutions together? does it ever go stale and not work?