While everyone's hair is different and reacts differently, I can personally say that I've never had a problem re-dying my hair a day or two after I've already done so. But whats OK for me may not be OK for your hair. I'd suggest testing a strand or two out in a not so noticeable place on your head before doing the whole thing. Plus it also depends on your current color and what you want to re-dye it to.

I believe 3 weeks. Who knows, by then you may like it.

If you’re prompt, the damage can probably either be minimized or completely reversed. Generally, hair color takes from 48 to 72 hours to set into the cuticle. However, because this window is so brief, before you begin experimenting with hair color removal, consult with a professional stylist. If your hair color problem resulted from an at-home application, start looking for help from the maker. Most major manufacturers have a consumer help line. You’ll find the phone number either on the box or in the instructions pamphlet. 1. Almost too simple to be true, but hot water sometimes fades chemical hair colors. 2. Volume shampoos and gels are often designed to blow open the hair cuticle. Although they won’t completely remove hair color, they may speed up the process. 3. Hot extra-virgin olive oil also may help strip chemical colors. However, do be careful. You don’t want to soak your head in boiling oil! 4. Get out the scissors. A short cut can minimize hair color problems. Your stylist can suggest one that will camouflage old color with new hair growth. 5. Put on a scarf and head to the nearest open-all-night super-store. The red in tomato juice may help neutralize green hair color. If your hair color came from a product that was chlorine enhanced, a special chlorine removal shampoo may help tone it down. A couple of hair color removal products are worth considering: One ‘n Only Colorfix – Made to remove permanent hair color and may even be used to correct color in specific areas. Clairol The Uncolor System Haircolor Remover – A semi-permanent hair color remover that Clairol says is gentle, quick, and easy. Tips for successful hair color removal: 1. Always strand test before you try any hair color removal 2. Deep conditioning with a low pH conditioner after hair color removal helps protect your hair as well as return it to natural softness and shine. 3. Remember to protect your clothing from hair color removal products. Even tomato juice can leave a nasty stain! 4. Precisely follow the directions on all hair color removal products. 5. Do not use hair color removal products on henna. Henna is unpredictable and can leave you with unusual results! 6. Keep hair color removal products away from your eyes. Don’t ever use them on lashes or brows. 7. Don’t use bleach for hair color removal. Bleach helps artificial colors penetrate deeper into the hair shaft and weakens the hair shaft, causing even more damage. Source:http://www.haircoloringguide.com/removal.htm

I have always heard 6 weeks to prevent hair damage from over-proccessing. Not sure if it safer to do it any sooner than that.

2 WEEKS so you dont ruin your hair.

I've done it the same day and never had a problem as long as you're going darker.The reddish brown or mediun golden brown cover well if you got too brassy. Good Luck.

I've colored it a darker color the same day. Worked ok. Make sure you have a great conditioner though!

You have to be careful to make sure that the new color will not interfere with the old color, chemistry wise/base color wise..if it does you could end up with some pretty funky color...certain base colors do not mix with other base colors..my advice would be to go to your nearest Sally Beauty Supply and ask someone there. Check to see how much ammonia is in the hair color. Often it is higher than Windex if you hair is healthy, not brittle, falling out, and if your scalp can handle another coloring, it will be OK to go ahead and redo your hair...after that, i wouldn't recommend doing it again for another 6 weeks. Once you get the desired color, you should only apply color (when you do a touch up) to the roots of your hair.