I have a Minolta SRT-101 for 35mm photography. I always cock the shutter right before taking a picture, however, if I decide not to take a picture what harm will it do if I have it cocked for longer periods of time? How long can I leave the shutter ready to fire before it starts to become inaccurate? Would I be able to leave it like this overnight or for a week?
I have been doing this stuff since the 1950’s, I have never actually seen damage to a camera due to the springs taking a set due to prolonged cocking. Not to say that can’t happen as I was taught not to leave springs cocked for extended durations (storage). In my opinion, you can safely use photo equipment paying little attention to how you leave the springs. If you know you are going to shelf an item, try and remember to activate the shutter so the spring will not be tensioned for the duration of the storage. I think it is safe to say, if you forget, it’s no big deal. I have retrieved cameras off the shelf that have been cocked ready for use, every one operated OK for me.
I would not lose sleep over it.
There are a number of film cameras - Rollei 35 in small and Bronica ETRSi in medium format come to my mind - that actually require you to cock the shutter after shooting. Rollei will not let you retract its little lens and Bronica will not let you swap lens without winding.
In both cases it is by design: you are meant to be ready to shoot the moment you pick up your camera (the Bronica also wants to ensure that both the lens and body are in the same state - wound / unwound). The springs of the shutter mechanism were designed to be kept in tension for extended time.
From a metalurgical standpoint, it isn't tension that causes a spring to lose strength, but repeated tension and relaxation. So leaving it either relaxed or under tension won't effect the strength of the spring that much over time. The parts that the tensioned spring is pressing against might fail if they are flawed or badly engineered. Like Jindra says, "I would not lose sleep over it."