Every city is different and your mileage may vary. A lot is dependent on how properly staffed your city’s planning staff is and how familiar your architect is with that city’s code. The city might be slow because they are low on manpower. If the design is poor you might have to submit multiple times to address the comments and revisions. Your contractor might also have questions during construction because of that and slow down the building process.
Junior ADU will range quite a bit. It depends on the scope of work. Sometimes it’s as easy as slapping up a drywall and maybe you don’t even bother to go through permitting it’s a simple remodel. Sometimes you have to rework the plumbing and electrical to make sure it meets building code.
Ground-up detached ADU by far takes the longest. You are essentially building a new tiny house, pouring new foundation for it along with all the utility connections. If you are doing ADU as an addition it might take a little bit less time than detached.
Thinking about saying “I do” to ADU? Contact me for a free consultation and tap into architects and contractors in my network. Check out my other resources on ADU’s.