You should probably let your new dreads go for at LEAST a week before you wash them for the first time, two weeks if you can stand it. When you first put your locks in, they will be only made up of loose hair stuck together in locks with the wax, until about 3-6 weeks later when they actually start to mat and dread. So they are pretty fragile in the first few weeks and don't take to getting washed too well. The longer you can wait, the better, but if you have to, it's ok to wash them sooner than that, and use the dread shampoo.