How long does it take to get used to the feel of dentures when you get them for the first time?

At the beginning, dentures are a little difficult to adjust to but will become more natural within a few days. If you have been using temporary dentures while waiting for the permanent ones, the transition will be much easier.

That depends upon how well the dentures fit and the individual involved. If they fit well you should become accustomed to them within a couple of weeks. However if the fit is poor you might not ever become comfortable wearing them.