What a useful information
The longer you can wait, the better. Red is notorious for being a hard color to keep without fading (but it's also one of the harder colors to remove - go figure). Go as long as you can before your first wash (at least 5 days, if you can manage it) and as long as you can in-between shampoos, in general. Let dry shampoo be your friend. When you do wash, use a gentle, sulfate-free shampoo. If you choose to refresh/touch up your color yourself, there are additives you can buy at your local beauty supply store that (supposedly) will help with maintaining your color (though I have not found them to be helpful). I have found that color depositing shampoos and conditioners (Joico makes both a red, and a copper, depending on what your color is) will help with fading, but they tend to be drying (but a deep conditioning treatment weekly helps).