It really doesn't need to take much longer than shooting with a medium format camera, once at a location I keep the camera on the tripod ready it's just a case of removing my backpack to get film holders & light-meter, although often I keep one in a pocket (when in the UK).
Originally Posted by c.w.
Having said that shooting LF is more disciplined, most people shoot far less exposures and spend more time finding the image they want to shoot. Often I'll find the shot, if the lights constant I might set up the tripod & camera, then wander about a bit before deciding on the shot, most times I've already put the tripod in the right spot. Now in comparison an MF user would most likely shoot more images and work around a subject more.
So now if we put that 20 minutes into perspective, it should take no more than 2 minutes to set up and actually make the exposure with an LF camera, the fact that you night spend 5 minutes or even an hour in the location is quite different, often I've gone out with an LF camera etc and spent 3 or more hours walking and never made an image.