Can a person act to prevent loss to another without their permission to preserve their right of redress due to time limits stated in a contract?

This is an interesting question and, because of the highly theoretical way in which it is framed, difficult to answer. As a general matter, which rights are personal to the holder of an "entitlement," a stranger to the relationship between the "entitlor" and "entitlee" has no right to exercise the latter's rights, and the "entitlor" could probably refuse to recognize the exercise of those rights. Of course, a possible workaround is for you to hold yourself out as "John's" agent. Under the law of agency, if John later ratifies your acts, then the other party may be bound, but you could be in trouble if John is unavailable or refuses to ratify. If I understand the second branch of your question correctly, you suggest that, since you and John have a common claim, you might have heightened standing to exercise John's rights on his behalf. I can think of no legal reason why this theory might be supported. As with all other matters in this forum, this is not legal advice, and you should consult an attorney regarding your rights and duties.