This is a Quora question I answered today.
Me personally, I would say about 3 days for things to sound normal. And even while I was adjusting to the artificial sound, I was overjoyed by the ability to hear things I’d forgotten about. Like, I came out of the hospital in May and thought “wow there’s a lot of birds about this morning!” After the third day I realised there are always lots of birds, I just hadn’t been hearing them the last few years!
I was young (about 25) and had only a very high frequency loss, which was relatively new at that stage. In my experience, it takes longer for people to adjust if they:
a) are older (as in 70+)
b) have had the hearing loss for many years before trying aids
c) have a more severe hearing loss, at multiple frequencies
d) are psychologically resistant to hearing aids
The more severe or long term the deafness, the more artificial the sound will be at first. This makes your physical adaptation more of a hurdle. Age is not always a factor but it can make processing new sound more difficult.
The most important factor to success, in my opinion, is the psychological resistance. The others can be mostly overcome if you can see the positives of wearing the aids and have motivation to rehabilitate.
However, the absolute vast majority of my customers are very happy to hear well again. All that varies is the amount of time/effort needed to help them in the early days.
If you are thinking of hearing aids or are very new to them, make sure you get that support and dive right in. Don’t put off wearing them daily. The more hours a day you wear them, the faster the adaptation will be.