The building time greatly depends on where your base is, thus how far are the base commodity sellpoints. Also, if you do it alone, it will take weeks, if not months. Especially tha fact you need approval and wait time for core upgrade 3 and 4, which upgrades are useful if you want to build factories, to store the commodities needed for manufacturing.
Also, don't forget to get inRP permission to build the base, or it will be destroyed fast.