>>390944471
First from-scratch avatar was around 400-500h starting with zero experience, probably a safe estimate

Assuming you want an anime avatar and not something simpler, you could learn from zero to a working stick figure avatar in an afternoon obviousl, but that's all you will know how to do.

Don't worry about "full avatar" now though. Get a good, high quality base model from booth or maybe gumroad and get familiar with blender/unity/subpainter as you customize it. First learn how the textures and materials work so you can change the colors in photoshop. Then move to blender and attach glasses or a hat or ears or whatever. Then try to make your own accessories (blender doughnut and other generic modeling tutorials will be useful here). Then consider making clothing to learn complex weight painting: most of it can be transferred from your base, but you'll want to touch it up. Move to the avatar's face and try making new blendshapes for original expressions. Maybe create new hair using curves and paths and so on. 

Little goals that are easy to achieve and a bit of ambition to keep your ultimate goal in mind will be enough. Eventually you'll get a "huh" moment when you realize you know 90% of what you need to just do it all from scratch yourself and can start any time. It's one of the reasons for the regular "dress-up" events, it gives people excuses.