I do not think there is an official length of time and if they do, no one knows what it is. Some have said they got rejections over it, others say they got requests for an updated form, while still others have said that IRCC allows for the current form and one older. Some say they have a month to three months leeway, while some also say that it depends on the person that looks at your file and if they are anal enough to have an issue with it. So the short answer is that no one really knows.
I personally submitted mine in January and it had outdated forms from March, but from what I see, the only difference is the legal disclaimer at the bottom, which does not seem so important. Therefore, you are probably fine with your submission.