The finish provides some corrosion resistance, and more importantly, good adhesion. It is typically used as the base for an organic coating. There are actually many kinds of conversion coatings, some based on chrome and some used on other metals. Sometimes it used as a final finish, but this requires the use of a very strong bath. Most paint applicators do not maintain a strong chrome bath because it is not required for paint pretreatment.
Steel requires a different pretreatment than aluminum.
It only takes a few hours to process and pack a part. Most coaters need anywhere from a few days to a few weeks to plan, process and invoice for projects. Lead times of longer than four weeks for painting are rare. Liquid paint is composed of pigment, resin, and solvent. Since painting is obviously quite different from anodizing, keep your metal supplier informed of finishing requirements.