If your scalp is oily enough, then it is okay to wash your hair one day prior to dyeing it. Avoid using any styling products to allow the dye to evenly penetrate your hair. The natural oils on your scalp are protective against the dye's effects, and they are the main reason for not washing your hair the same day as dyeing it.
There is no problem if you wash your hair before dyeing it. After all, you need to get rid of those accumulated particles and chemicals on your hair so that the dye would have an easy time working on our hair. This is as compared to trying to get past all those things to get its job done.