I work in an architecture firm that has a very heavy high-end interior design component. Having good modelling skills is crucial in our office, since we deal in a lot of custom furniture pieces and millwork.
I can't quantify the number of hours I spend modelling every week since it changes depending on the project.
The ability to iterate and react quickly to the interior designers ideas or the whims of clients is really crucial. The important skills that I would look for are: diverse modelling skills, good eye for composition, being able to analyze a physical sample and accurately replicate it as a material, general problem solving skills.
This is my process If an interior designer wants to use a specific furniture piece in a render.
1. I spend 5 min looking to see if there is a model available somewhere online either free or paid.
2. If a free model isn't available, I judge how long it would take for me to make the model... If i think it would take me more than an hour then we usually go ahead and purchase a model, since it doesn't make economic sense to pay me to make the model.
3. If there isn't an exact model I'll try and find a similar looking model and make the changes myself, like taking cushions from another couch and co-opting them in my new model.
4. I would say 50% of the time we can't find a specific model online and I end up make it myself.
5. That being said... I never model plants. It usually takes way to long, and there already quite a good selection online.
I usually do a first pass in regards to interior design. I work quiet closely with the interior designers and am usually part of the initial meetings with the principals of the office, so I have a good idea of the direction of the space before we officially start. I put in furniture, lights, accessories, and finishes based on what was discussed in the initial meeting. It is either adapted and iterated on, or completely scrapped and I start again.
I make my own textures; Either by scanning the samples that we have here in the office or by finding similar textures and finishes online. We have subscriptions to megascans and textures.com
Hope this gives you an idea. Let me know if you have any more questions!