I love the pattern! I think it would be helpful to make the baby version first. With the baby version there are no decisions to make really so you get a good idea how it's put together. The adult version requires working the numbers to fit you.
They can go really fast since they are garter stitch. I really couldn't guess at the number of hours, but I think you could do one in a few days if you knit a lot. I took about a week for this one and that included ripping back when something I tried didn't work.