Glen,
Planning varies according to the objectives of the shoot. I periodically work on nude studio series as allegory and these require fore-thought as you'd expect. Invariably I need to give the
model a precis of the role she is to portray and I need to ensure I have the appropriate stuff with me to take to the hire studio. Most frequently that has meant setting up a sea of 300 or so candles of late.
But outdoors I am happiest when I am as free as a bird. I'm something of a fan of the found object and after over 40 years of doing it I can set up, get my shot, pack and be back in the car in as little as 5 minutes. That, of course, is the exception rather than the rule because it is also very nice to take your time and explore the possibilities a motif has to offer.
Commercially I use a view camera all day to shoot for architects and with domestic architecture it is often necessary to be quick in order not to bother the home-owner unduly. As a rule I can get through 10 or 12 set-ups in an hour and a half. Mind you, not everybody works as quick as that.
At the other end of the scale the subject can dictate a slower process. I shot the Hoyts complex at Fox Studios and had to do interiors of the actual cinemas because they had re-introduced the dress-circle. The lighting was extremely dim even when lit. The guy at the lab looked at my trannies as they came out of the machine and asked how long the exposures were. "Three and a half pages of a novel at f16" was my reply. In other words, each actual exposure was over 20 minutes and I had taken a book and a torch so I could amuse myself while waiting. Biggest problem was that I only had time for a single exposure between each screening and the client wanted four originals and so there were many trips in and out of that auditorium. On another occasion I shot a building exterior at the Rocks in the pre-dawn glow with tungsten film. The exposure again was 15 minutes and at the end of an exposure the light had gone and so I had to set up a number of days in a row to get the shots I needed. Still, they want it and they pay for it and I enjoy doing it - what better thing for a boy to do?
So, to answer your query, like every other aspect of photography everything is variable and things are often not quite as they seem.
PS: I have also done 30 minute exposures on 35mm. And when I shot for Playboy and Penthouse in the early days the usual exposure on Kodachrome 25 for a girl sitting in a room was about 1/4 sec at f4. Time is the least of our worries.
Cheers,