Sounds like you're in an awesome position. I wish I could find a well-located 3-unit property in my market. My husband and I had to fight tooth-and-nail to acquire both of our 2-unit properties.
Not sure if you're asking...
1) How long it takes to set up a STR in terms of getting it furnished/stocked or..
2) How long it takes for a STR to realize it's full revenue potential (given whatever seasonality occurs in your market)
If 1) - It took me about 1 month to setup and furnish each of my 3bed/1bath Airbnbs. This is me working basically all day everyday with little to no help. I also have a 200 sq. ft. studio that only took me about 2 weeks.
If 2) - This is probably very market specific. I am in a metro market and exclusively list on Airbnb. In my experience, my 1st month revenue is about half what it should be. This is mainly due to intial discounts (20% of for first 3 guests), having to cancel reservations because of unexpected repairs, and less bookings since you don't have any reviews. Once a listing has 3 positive reviews it is smooth sailing (on Airbnb, in my market).