Idempotent Synonym with a Specific Condition?

I'm looking for a word that is a close synonym to both idempotent and redundant, but conveys two important differences from those words:

1. It is different from idempotent because it is not idempotent forever. After a period of time, a repeated application would have the same effect.
2. It is different from redundant because redundant carries a negative connotation of "not worth doing". The word I am looking for would carry the connotation of "worth doing once".

For example, you would describe the act of putting on sunscreen as this word. It's worth doing once, but you don't need to do it again until the sunscreen you've already put on has become ineffective. Other examples:

• Watering a houseplant in a pot with good drainage.
• Cleaning a room.
• Getting a haircut, or perhaps even a massage.

There are two different senses of idempotent.

In algebra, being idempotent has no temporal componet.

relating to or being a mathematical quantity which when applied to itself under a given binary operation (such as multiplication) equals itself

MW

In computer science, look at common examples, like this one from Wikipedia:

a request for changing a customer's address to XYZ is typically idempotent, because the final address will be the same no matter how many times the request is submitted.

That assumes a lineage or ordered transaction that isn't implied at all in the abstract algebra case. It is true that changing the address multiple times for a single request should result in the same system state given no intervening changes. Over time, that qualifier is less likely to be true, depending on context. If I pushed that change again 10 years from now, and your address had changed in the meantime, the operation fails to be idempotent, and reverts your address. This reality is typically ignored, but look at how databases like couchDB handle this: to update a record you must have the ID of the most recent version. The ID changes with each update, blocking the non-idempotent address change, and leaving it to the application to resolve.

Outside the mathematical sense, idempotent changes put a silent qualifier on the "period of time" you reference, and covers your cases reasonably well.