yes most inman aligner cases should take around 10- 12 weeks to complete. It is too uncomfortable to wear two inman aligners in one go, so if you need both arches corrected then it can take longer and it might be worth considering fixed braces.- and it might be cheaper in some practices to do so.
You do not need to wear your inman aligner 24 hours a day though. Many of my patients faced the same issue and simply removed it when they needed to speak and replaced it when they had some quiet time. Even 16 hours a day will often be enough.
18-20 is the optimal amount of time and you should not actually wear it any longer.
Im not quite following you on what you mean by the small amount of time to fit- do you mean the actual time it takes to fit the aligner and give you the instructions?