Presumably utility is measured by someone who exists at the moment of action? If you do something on Tuesday that you want to do, that is what matters. You may regret having done something else on Monday, or having to do something you currently don’t like on Wednesday, but it is sort of irrelevant. If your UF is not stable, it is probably not a good description of what is going on.
If the Monday creature is indeed able to fix its preferences, how do you compare utility between the two alternatives since they have different UFs?
Presumably utility is measured by someone who exists at the moment of action? If you do something on Tuesday that you want to do, that is what matters. You may regret having done something else on Monday, or having to do something you currently don’t like on Wednesday, but it is sort of irrelevant. If your UF is not stable, it is probably not a good description of what is going on.