There’s an old quotation from some artist or other…when asked “How long did it take you to do this painting?”, he said, “My whole life.” Meaning that you’re never done learning…but, depending on how much time and effort you put ino it, you can be producing some nice stuff within, say, a month.
If you already draw a lot, and maybe paint, that will help. I don’t think that photorealism is necessarily the goal of 3D, in fact, my favorite Blender artist is Nick Towers http://pages.zoom.co.uk/nick.towers/ and not just bcause we share a first name. So do the tutorials, have fun, and keep a critical eye on your work and others’ and ask a lot of questions.
Oh, yeah, after trying unsuccessfully to learn Lightwave for a year, a friend recommended that I try Cinema 4D and I did my first animation in that in about a month. Sometimes it’s just which 3D application works with the way you think…