Color negative film balance is as constant over the years as color reversal film! Changes with keeping are similar to what is seen with reversal film, but in general are less deleterious to the imaging than with reversal films.
These statements are based on 32 years in the business and tests of films made over a 50 year period. I can print 50 year old films at about the same balance as modern films within about a 10 Y.
This refers to Kodak film primarily, but the Fuji films that I have tested fit closely into this category. Agfa films generally have fallen outside of this for both color balance and changes with keeping.
In my little experience there is a change in color balance if it takes too long between exposure and development (months). This has happened to me in the same roll, being left in the camera for long time with some exposed frames, then expose the rest of it. (pictures with similar lighting conditions)
In my little experience there is a change in color balance if it takes too long between exposure and development (months). This has happened to me in the same roll, being left in the camera for long time with some exposed frames, then expose the rest of it. (pictures with similar lighting conditions)
I wonder if this was due to other reasons. My wife takes many months to use a roll of 24. Typically the first shot is the New Year party and the last the Christmas day celebrations and I have never seen a change in colour balance.
No doubt others will agree or disagree, hopefully with reasons.
The latent image of a color negative film and a color reversal film are about equal for stability. The color negative is actually a bit better due to the fact that any changes are able to be damped out in printing.
I would say that at normal room temperatures, the images on exposed film should last for at least a year with no significant change as far as amateur purposes are concerned.
The discriminating professional should process the film as soon as possible and keep the film as cool and dry as possible.
The changes I have experienced are very small and appreciable only in a contact sheet or if you don't change filtration in the enlarger.
Also, again in my experience, professional films like portra 160 nc are more sensible to this (the old Kodad vericolor was the most sensible). It hasn't happened to me with consumer grade film.
Temperature and humidity were above recomended, so they might be factors to consider.